Prepare the dough:

1. In a bowl, combine flour, sugar, baking powder, and salt.
2. Add the butter and rub it into the dry ingredients until the mixture is crumbly.
3. Mix in the eggs, vanilla, and lemon zest until a smooth dough forms.
4. Divide the dough into two portions, wrap in plastic wrap, and refrigerate for 1 hour.

Make the pastry cream:

1. Heat the milk with vanilla in a saucepan until warm.
2. In a bowl, whisk together egg yolks, sugar, and cornstarch.
3. Slowly pour in the hot milk, whisking continuously.
4. Return the mixture to low heat and stir until thickened.
5. Remove from heat, stir in rum (optional), and let cool completely.

Assemble the cake:

1. Preheat the oven to 350°F (180°C) and grease a 9-inch cake pan.
2. Roll out one portion of the dough and press it into the bottom of the pan.
3. Spread the pastry cream evenly, then add a layer of cherry jam.
4. Roll out the second portion of dough and place it over the filling, sealing the edges.
5. Brush the top with a beaten egg for a golden finish.
6. Bake for 35-40 minutes, until deep golden brown.
7. Let cool before slicing, then dust with powdered sugar before serving.

Notes

• Cherry jam is the traditional filling, but you can use blackberry jam or pastry cream alone for variation.
• The dough is similar to a shortbread, so handle it gently to prevent cracks.
• For a crispier texture, chill the assembled cake for 15 minutes before baking.
• Pairs perfectly with coffee or a glass of sweet wine!