To prepare the jam tart, start by softening the butter, being careful not to burn it. In the meantime, sieve the flour into a large bowl or basin (leave aside 2 tbsps of the flour). Add into a bowl the baking powder and the vanilla extract and blend.

Pour in the butter, the egg yolk, the sugar, the lemon zest and the cognac and knead the pastry with your hands, until the ingredients are combined and the pastry is smooth and soft. Do not overwork the dough.

You can either make one jam tart, or individual little tarts, using the appropriate sized trays.

To make one jam tart separate the dough in two pieces; use the one half to form the bottom of the tart. Butter the bottom and sides of a tart tray (30cm diameter). Dust a work surface and a rolling pin with flour. Roll out half the dough to fit the bottom of the tart pan approx. 1 cm thick.

Carefully roll your pastry around the rolling pin and then unroll it over the tart pan and ease the dough into the dish, pushing it into all sides, and trimming the remaining dough. If the pastry tears or breaks, just patch it up.

Roll out about 1/3 of the remaining pastry to make a strip (about a finger's width), brush it with the egg white and place all around the raised sides of the tart pan, pressing it gently to join with the base.

Spread evenly the jam over the base. Roll out the remaining dough into thin strips, brush with egg white and decorate the tart, placing them in a latticework pattern.

Bake the jam tart in preheated oven at 175C for 30-40 minutes, until nicely colored. Let it cool down for a while before serving, so that the jam thickens.