Pulse the flour, sugar, salt and baking powder in a food processor 3 or 4 times to blend. Scatter the butter over the flour and process until the mixture looks sandy and you can’t see any butter chunks.
Whisk together the egg, yolk and milk. Add to the flour mixture and pulse a few times until the dough just begins to come together (but not until the mixture forms a ball over the blade which will toughen the dough). Add some ice water drop by drop if it seems dry. Remove the dough from the workbowl and knead it gently to form a ball. Flatten it into a disc, wrap in plastic wrap and chill in the refrigerator about 1 hour until firm but not hard. If the dough gets too cold and seems hard, leave it out for 15 minutes until it’s workable.
Lightly dust the dough with flour and put it on a lightly floured surface (a smooth countertop is ideal). Slice off ⅓ of the dough and set it aside, covered loosely with a floured towel.
Place the remaining 2/3 dough between two large pieces of lightly floured parchment paper or plastic wrap and roll out to a 12-inch diameter circle. Carefully peel off the parchment, roll the dough onto the rolling pin and unroll over a 9-inch tart pan. Press the dough into the pan and up the sides, trimming the top edges of the dough flush with the pan by running the rolling pin over the top.
Spread the jam evenly over the tart.
To make the lattice:
Roll the reserved 1/3 portion of the dough on a floured surface to 3/8-inch thickness. Cut into ½-inch wide strips with a fluted pastry cutter or small, sharp knife.
Lay the strips in a diagonal lattice pattern over the tart, starting in the center with the longest piece, trimming if necessary. Pinch the dough where the edges meet around the diameter of the pan. Put the tart in the refrigerator and chill 1 hour.
Preheat oven to 375 (190 C) degrees. Bake 30 minutes, or until the lattice is golden brown and the jam is bubbling.