First of all prepare the pastry cream. Bring the milk to the boil with the vanilla pod and lemon rind in it; then leave it to cool down. In the meanwhile, beat the egg yolks with the sugar until light and fluffy. Stir the flour into the beaten yolks, a little at a time, making sure it is well amalgamated. Then very slowly pour in the cold milk (from which you have removed the vanilla pod and lemon rind). Put the mixture back on the stove, over a very low heat and, stirring constantly with a wooden spoon, bring the pastry cream almost to the boil, removing it from the heat just before it begins to do so. If any lumps should have formed while cooking, whisk the pastry cream slightly until it is smooth and homogenous.
Now prepare the dough. Beat the softened butter (take it out of the fridge at least an hour beforehand) with the sugar, egg and finely chopped almonds. A little at a time, mix in the sieved flour and baking powder. Form a ball of soft dough and divide it in two. Using one half at a time, use your hands to spread out the dough in a shallow, non-stick, baking tin (like a “pizza pan”) measuring 30 cm in diameter (well-greased with butter and sprinkled with breadcrumbs). Cook both of the disks, one after the other, in a preheated oven at 180 °C for about 10 minutes (until they turn a nice biscuit colour). Remove the focaccia from the baking tin when they have cooled slightly and transfer them onto a round serving dish; take care not to break them, they are very crumbly.
Spread the cold pastry cream on one of the focaccia disks; slide the second one on top and press it slightly onto the pastry cream. Sprinkle the icing sugar over the surface, using a tea strainer to sift it. If you serve it straight after baking, the focaccia, which has a very crisp crust, tends to crumble as you slice it (it’s still delicious, but not quite as good to look at). If you wait a couple of hours, the pastry cream will soften it slightly and the focaccia will slice perfectly.