Preheat oven to 340°F / 170°C.
Combine flour and baking powder in a bowl and set aside.
Add butter and sugar to your mixer's bowl and with the paddle attachment on beat for 4 minutes over medium speed.
Add the egg and mix to incorporate.
Add the vanilla, salt, and milk. Mix until combined.
Add the flour in gradually and once fully incorporated turn off the mixer.
Rest dough: Shape the dough into a round ball and wrap it in plastic wrap. Place in the fridge for 1 hour.
Roll the dough: Take about ⅔ of the dough and shape it into a round ball. Add the remaining ⅓ back into the fridge. Using a rolling pin, roll open the dough ball on a piece of parchment paper. Open to a large 30 cm round disk. Gently roll the dough loosely around the rolling pin. And then unroll it over the tart pan. Or transfer the dough using the parchment paper and swiftly overlap over the tart tin. Use a 28 cm (11-inch) tart pan. Make the tart: Press the dough firmly into the bottom of the pan and up the sides. Trim any excess dough. Prick the bottom of the dough with a fork a few times. Then add the cooled jam and spread it evenly with a spoon.
Make the topping: Take small pieces of the leftover dough, shape them into balls, and then into cords. Pat lightly each cord with your fingertips to flatten it slightly. Then place it on top of the pie criss-cross to create a latticework.
Bake: Bake the tart for about 30 to 35 minutes until golden on top.
Serve: Serve topped with icing sugar or a scoop of ice cream or Greek yogurt.