Separate the egg yolks from the whites. Place the egg whites in a bowl and beat with an electric mixer for about five minutes, until they are very foamy. Add half of the sugar and continue beating until you have stiff, glossy peaks. Set aside.

In another bowl, beat the egg yolks with the remaining sugar until the mixture is pale and triples in volume. Add the vanilla extract, lemon zest, and milk, mixing until well combined.

Now, gently fold the beaten egg whites into the yolk mixture, a little at a time, using a spatula to keep as much volume as possible. Once fully combined, sift in the flour and baking powder. Carefully fold everything together, just as before, to keep the batter light and airy.

Grease a 9-inch (23 cm) cake pan with butter or nonstick spray. Pour in the cake batter and bake in a preheated oven at 350°F (180°C) for about 45 minutes, or until done. Remove from the pan and let cool completely.

Line the same cake pan with plastic wrap, making sure it covers the bottom and sides with extra hanging over the edges. Place the cooled cake back in the pan. Use a knife to poke holes all over the surface of the cake, going all the way to the bottom, several times.

To make the sauce, simply mix all the ingredients together until well combined. Pour the sauce evenly over the cake, then fold the extra plastic wrap over the top to cover. Refrigerate overnight, if possible. The next day, you'll have a super moist cake.

I whipped a little heavy cream with powdered sugar and decorated the top as I liked, but this cake is so good it really doesn't need any decoration.