This tart boasts a filling of blueberry jam, almond paste, and sliced almonds.
In the bowl of a food processor, pulse flour, sugar, cornmeal, and salt to combine. Add butter and stir with a wooden spoon to coat butter cubes in flour. Pulse the food processor several times until mixture resembles coarse oatmeal. Add egg and 2 tablespoons milk; pulse until dough begins to come together in a ball (add 1 more tablespoon liquid if needed). Transfer dough to a lightly floured work surface and knead briefly to shape into a disk about 5 inches across. Wrap in plastic and refrigerate at least 30 minutes or overnight.
Using a lightly floured rolling pin, roll dough into a shape ½ inch wider than the tart pan you’re using (we used a 9-½-inch round pan). Fold dough loosely in half and transfer to tart pan. Line pan with dough, being careful not to stretch it. Trim any excess dough from pan rim, leaving a blunt, neat edge. Gather trimmings into a ball (it should be about the size of a ping-pong ball). Wrap tart and small dough ball in plastic and refrigerate at least 1 hour, or up to 2 days.
Preheat oven to 375°. Remove tart pan from refrigerator. Between two sheets of wax or parchment paper, roll almond paste into a circle the size of the pan and place in bottom of pan. Top with an even layer of jam. Grate chilled pastry ball onto filling. Sprinkle almonds over top. Bake on a rack in center of oven until pastry is golden, filling is bubbly, and almonds are toasted, 40–50 minutes.
Transfer to a wire rack to cool. When tart is completely cool, dust with confectioners’ sugar. Serve at room temperature.