Beat the eggs with the sugar until whitened. Add the oil and stir a bit more. Add the lemonade and the flour mixed with the ammonium bicarbonate and vanilla.
Stir until homogeneous with a spatula or spoon.
Pour it into a 11 3/4″ (30 cm) diameter tray with baking paper.
Bake in a preheated 356°F (180 °C) oven about 20-25 min. or to a golden color. Check with a toothpick, it needs to come out dry.
Bake another 2 layers this way. Leave them to cool.
For the cream, put the milk to boil after setting aside 4/5 cup (200 ml) of it.
Beat the eggs with the sugar, gradually add flour and the set aside milk. Stir well, to obtain a thick mixture without lumps. Add this to the boiling milk and stir until thickened but not too much. Add the vanilla and butter and stir until it melts.
Start assembling the cake without waiting for the cream to cool.
If you don't have a cake form, arrange it in a tray in which you've put cut out pieces of baking paper and placed along the sides. The cake is quite a tall one.
Once it cools afterward, you can invert it into a platter.
Put the 1st layer on, poke holes all over it with a fork to allow the cream to seep in and make the cake juicier. If you're going to be inverting it, don't smear the top layer. In that case, cover the rest of the cream with plastic wrap and once the cake hardens and you've inverted it, then smear it.