Simply Amazing Magic Custard Tart

Amazing and magic are two words I don't use lightly when it comes to recipes, but I must make an exception here (and also break my rule of featuring only original recipes on this blog). This trembling, luscious custard tart, with its delicate cakey topping, makes itself in the oven, and it's one of the most interesting recipes I've come across in years.

Simply Amazing Magic Custard Tart, with a soft cake topping, a rich custard base
 and my addition of burned-sugar stripes. You will notice that the custard in the
 slice on the right looks firmer than the custard in the two slices on the left.
The right-hand slice was cut from the very edge of the dish, and the other two from
 its middle. So the next time I made this dish, I placed it in a bain-marie, which helped
 to even out the texture. Plate by David Walters. 

I made this more elegant version of Magic Custard Tart - plated here in a puddle
of Jersey cream -  in a bigger (and circular) flan dish. I think I prefer the squares
 in the picture above, however, as the custard base is thicker and softer.

You can't really see it clearly in this picture,
 but the custard separates into two distinct layers.
 In this version,  I sifted the flour twice, which
created a thicker & lighter cake topping. 

I noticed this recipe appearing in various forms on Pinterest a few weeks ago, but couldn't help feeling doubtful about it. How can an alarmingly thin batter of eggs, flour, melted butter, vanilla and milk transform itself into a creamy custard tart of perfection? What kind of wicked kitchen alchemy is this? Well, I don't know the exact science behind this, although I have tried - in the process of testing and re-testing it - to figure out how it works.

I'm going to give you the recipe right away, but if you're interested in my testing notes, my tweaks, the origins of this recipe, and some important watch points, please scroll down to the bottom of this post to read my Cook's Notes.

I've given these ingredients in both grams and cups/ml, but I suggest that - for perfect results - you weigh the ingredients using a digital scale.


If you don't have a scale, use cups & tablespoons marked in  millilitres, and be sure to measure exactly, levelling off the tops with a knife, and not pressing down on the ingredients.

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Simply Amazing Magic Custard Tart 

125 g (125 ml) butter

2 cups (500 ml) full-cream milk

4 large, fresh, free-range eggs, at room temperature
150 g (about 155 ml) caster sugar 

115 g (about 225 ml) cake flour, sifted
a drop or two of lemon juice

1 tsp (5 ml) vanilla extract or essence

the finely grated zest of half a lemon (about 1 tsp/5ml)

To top:

icing sugar, for decorating

fresh strawberries or raspberries

Heat the oven to 160 ºC, fan off.  Grease a deep ceramic or glass baking dish measuring 20 x 20 cm, or coat its inside generously with baking spray.

Cut the butter into cubes, place them in a pot or microwave-safe bowl, and add the milk. Warm the mixture on the stove or in the microwave, until all the cubes of butter have just melted. Stir well, then set to one side.

Separate the eggs into two large bowls. Squeeze two drops of fresh lemon juice into the bowl containing the egg whites. Using a hand-held electric beater (see Cook's Notes, below) whisk the whites until just firm. They should form soft, snowy peaks that hold their shape, but they mustn't be at all stiff or dry.  Set the bowl to one side.

Add the sugar to the egg yolks and, using the same beater (no need to rinse it), whisk at a medium speed for about two minutes, or until the mixture is pale, thick and creamy. Add the sifted flour and the luke-warm butter/milk mixture, bit by bit, and alternately, beating all the time at a medium speed.  Make sure the butter/milk mixture is just warm, or it may curdle the eggs.

When you've added all the flour and butter/milk mixture, beat at a low speed for another 30 seconds, or until slightly foamy. Stir in the vanilla essence and grated lemon zest.

Now comes the only tricky part of the recipe: incorporating the beaten egg white. It's virtually impossible to fold in the egg white, as you would do with a thicker cake mixture, because the batter is so thin.  So here's how to do it: scoop a quarter of your beaten egg white into the mixture and, using a wire whisk, briskly beat it in to lighten the batter. Now tip in the remaining egg white and use your whisk gently - very gently - to incorporate it into the batter, using the tip of the whisk in a light spinning motion.  When the mixture seems reasonably well combined - don't worry about any small egg-white lumps and bumps on the top - pour it into the greased dish.

Use the tip of the whisk to break up any lumps of egg white on top, then place the dish in a deep baking tray. Fill the baking tray with hot water so that it comes to two-thirds of the way the sides of the dish and place in the oven.

Bake the tart at 160 ºC for 45-60 minutes, or until it is a rich brown on top, and still slightly - but not alarmingly - wobbly in the centre. The centre of the mixture should give a reluctant shudder when you jiggle the dish.  Keep a careful eye on it, as the topping turns very brown in an instant.

Immediately remove the dish from the bain marie and allow to cool. You can serve this warm with custard or whipped cream, but it's best chilled overnight in the fridge.

To serve and decorate: generously sift icing sugar all over the top of the cake. Cut into squares, and serve cold, topped with fresh fruit.  For instructions on how to mark the top of the tart with a hot skewer, see below.

Serves 6

A marking of burned sugar adds a satisfying caramel crunch to
the tart. See Point 9, below. 

Cook's Notes 

1. I tested this recipe four times, adjusting the ingredients slightly with every try - less sugar, more flour, and so on. I also tried making it with Stork baking margarine - my late mother-in-law Audrey always insisted that this produces the lightest cakes - but this version wasn't as light and delicious as the buttery ones.
2. In these notes I've included some important tips that will help you to perfect this dish. Having said that, it may - curiously - not be important for you to heed this advice. Every time I made this, the result was slightly different, but not once did the recipe fail. It's pure kitchen magic. See Point 4, below. 
3. The significant changes I made to the recipe were to add lemon zest; to bake it in a bain-marie to prevent the outer edges of the custard browning; to add a few stabilising drops of lemon juice to the whites; and to warm the milk and butter together. (The recipes I used as sources warmed/melted the milk and butter separately, which required an extra bowl. I figured that warming them together would ensure that both ingredients are at exactly the same temperature when they go into the egg yolks.)  I also added a decorative topping of burned-sugar stripes (see Point 9, below), which add a lovely delicate caramel crunch.
4. Because the batter is so thin, it's difficult thoroughly to incorporate the beaten egg whites without losing some volume. A light touch is important here but, even so, the recipe is quite forgiving - if you watch the video mentioned in Point 10, below, you'll notice that the batter is handled quite roughly, with no ill effects. 
5. Carefully measure out all the ingredients (I place them on small squares of baking paper) before you start with the recipe. This will allow you to put the cake together very quickly, so it doesn't lose any volume. Place it straight into the oven once you've added the beaten egg whites.
6. Be sure to double-sift the flour -  I did this in my final test and the cake layer was noticeably thicker and lighter (see the third photograph, above). 
7. You can use a normal wire whisk to make this dish, and plenty of elbow power, but a hand-held electric whisk is best. I tried making this, the first time round, in my Kenwood Chef, but it was too powerful, and the egg whites were too stiff to mix easily into the batter. 
8. There are some interesting chocolate versions of this recipe here, here and here, but I haven't tried them.  
9. To make caramel stripes on the tops of the squares, heat a flattish metal skewer in a high flame.When it is very hot, press it lightly into the icing sugar layer to form caramelised stripes. You'll need to keep re-heating the skewer, as it cools down fairly quickly.  Do this shortly before serving the squares, or the caramel may turn sticky. It's easiest to do this once you've cut up the tart, but quicker to mark the entire slab in one go. I did this by easing the whole tart - which was very cold - from its glass baking dish. First, run a sharp, thin-bladed knife around the edges to loosen them. Then stand the dish up on its side so it's vertical, and wait until the vacuum below the custard layer releases. Let the whole slab of tart fall into your palm, then gently slide it onto a board. 
10. I can't pinpoint the original source of this recipe. Most of the more recent recipes on food blogs and Pinterest give as their source this recipe & video by Spanish food blogger Mabel Mendez. After some digging, I discovered that this dish is of Romanian origin, and that there are dozens of online versions of it written in that language.  It's called 'Prajitura Desteapta' (roughly translated by Google as 'Smart Cake'.)  Here's an example of a recipe written in Romanian, with some useful step-by-step pics.    

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