Whisk the flour, sugar, baking powder, and salt together in a mixing bowl.

Cut the cold butter into the flour mixture with your fingertips or a pastry cutter until it looks like coarse crumbs.

Add the egg yolk and vanilla extract, mix with a fork, then add cold water 1 tsp at a time until the dough just holds together when pressed.

Divide the dough into two pieces, about two-thirds for the base and sides and one-third for the lattice. Flatten into disks, wrap, and chill for 30 minutes.

Beat the softened butter and sugar together in a bowl until pale and creamy, about 2 minutes.

Add the eggs one at a time, beating well after each, then mix in the almond extract and lemon zest.

Fold in the almond flour until the filling is thick and spreadable, like soft frosting.

Heat the oven to 175C / 350F and grease a 23 cm / 9-inch tart pan with a removable bottom.

Roll the larger dough disk on a lightly floured surface to about 3 mm thick. Press it into the base and up the sides of the tart pan, trimming excess.

Spread the almond filling evenly over the pastry base.

Roll the remaining dough and cut into strips about 1.5 cm wide. Weave them loosely over the filling in a lattice pattern, then brush with the egg wash (yolk whisked with milk).

Bake for 35 to 40 minutes, until the lattice is deep golden brown and the filling is set with just a slight jiggle in the center.

Cool in the pan for 15 minutes, then transfer to a wire rack to cool completely before slicing.