In a medium mixing bowl combine flour, sugar, salt and baking powder. Mix with a whisk until incorporated. Add the egg and butter and mix until incorporated (the dough will be fairly "rough" at this point).

Turn the dough out onto a lightly floured work surface and gather it into a ball. Form the dough into two disks, one slightly larger than the other.

Wrap each disk tightly in plastic wrap, and refrigerate for at least 1 hour, or until well chilled (overnight is fine). Remove the dough from the refrigerator 30 minutes before rolling it out.

Carefully wrap the dough around the rolling pin and drape it over a 9-inch fluted tart pan or round pie dish. Gently press the dough into the bottom and up the sides of the pan.

Use the rolling pin or the flat of your hand to press around the perimeter of the pan to cut off any excess dough. 

Heat the oven to 350 degrees F.

Spoon the jam and lemon zest filling (or Italian pastry cream) into the shell and smooth it with a spatula.

Roll out the remaining dough portion into a 10-inch round about 1/8 inch thick or slightly thicker, and use a fluted pastry wheel or pizza slicer to cut it into 3/4-inch-wide strips, or simply cut it into strips, or make ropes by rolling with hands.

Carefully place the strips over the filled tart in a lattice pattern (not woven simply lay piece on one another), gently pressing the ends of the strips into the sides of the pan. Use the flat of your hand to gently cut off any excess dough.

If desired, sprinkle the top with sliced almonds 

Bake the crostata for about 30 minutes, or until the crust is golden. Remove from the oven and let cool to room temperature. Mangia! (Eat!)