Preparation

Make the filling

• Combine the sugar, lemon juice, and 1/2 cup water in a 3-quart saucepan. Bring to a boil over high heat, stirring occasionally to dissolve the sugar, about 2 minutes. Add the cranberries and lower the heat to medium-low. Simmer until the cranberries have popped and the liquid is syrupy, 10 to 12 minutes. Stir in the apricot jam and simmer until the jam melts, about 1 minute more. Remove from the heat and let cool completely.

Make the shortbread

• Position a rack in the center of the oven and heat the oven to 325°F. Spread the almonds on a rimmed baking sheet and toast until warm and fragrant but not yet brown, about 5 minutes; let cool completely.
• In a food processor (with at least a 10-cup capacity), combine the nuts with 2 Tbs. of the flour. Pulse until very fine but not powdery, 20 to 25 short pulses. Transfer to a large bowl and stir in the remaining flour, the cornmeal, and salt.
• In the food processor, combine the butter, sugar, lemon zest, vanilla, and almond extract.
• Pulse until creamy, 10 to 20 short pulses. Add the egg yolk and pulse a few times to combine. Add the dry ingredients and pulse, scraping down the sides as necessary, just until a soft dough forms, 30 to 40 short pulses. Turn the dough out onto a piece of plastic and divide.
• Lightly coat a round 91/2 x1-inch fluted metal tart pan with a removable bottom with cooking spray. Press half of the dough evenly onto the bottom and up the sides of the pan. Cover with plastic wrap. Form the remaining dough into a disk and wrap in plastic. Refrigerate the dough and the tart shell until very firm, at least 30 minutes.
• Prick the bottom of the tart shell all over with a fork and bake on a heavy-duty baking sheet until firm, dry, and just starting to turn golden brown around the edges, 30 to 35 minutes. The shortbread will have puffed up during baking, so use the back of a spoon to gently press down the bottom of the crust to create enough space for the cranberry filling. Spoon the filling into the tart and spread evenly.
• Crumble the remaining shortbread dough over the cranberries in pebble-like pieces, covering the filling. Bake until the topping is firm and golden-brown, 30 to 35 minutes. Cool completely on a wire rack.
• Carefully remove the tart rim. Slide a long, flat spatula between the pastry and the pan bottom and transfer the tart to a serving platter. Dust with confectioners’ sugar, if using, just before serving.

Make Ahead Tips

The dough disks can be refrigerated up to 2 days, wrapped tightly in 2 layers of plastic wrap.

The dough can be frozen for up to 2 weeks: Put the plastic-wrapped dough in a zip-top bag, seal, and freeze. Thaw the dough overnight in the refrigerator before proceeding with the recipe.

The finished tart can be wrapped in 2 layers of plastic wrap and stored for up to 2 days at room temperature.

The finished tart can be frozen for up to 2 weeks: Transfer it to a 10-inch cardboard cake round, wrap tightly in 2 layers of plastic wrap and then in foil, and freeze. Up to 10 hours before serving, remove the foil but not the plastic wrap from the tart and thaw at room temperature. When completely thawed, remove the plastic wrap. For freshly baked flavor, warm the tart in a 300°F oven for 10 to 15 minutes. Cool completely before slicing.