Step 1

Pulse ¾ cup almonds, salt, and 1/3 cup demerara sugar in a food processor until finely ground. Add flour and lemon zest and pulse just to combine. Add butter and pulse until mixture is the texture of coarse meal with a few pea-sized pieces of butter remaining.

Step 2

Transfer mixture to a large bowl and make a well in the center. Add egg yolks, milk, and almond extract, if using. Blend with a fork, then gradually incorporate dry ingredients, mixing just until liquid has been absorbed. Work mixture with your fingertips, adding more milk by teaspoonfuls if needed, until dough comes together in moist clumps and no dry spots remain (dough will look crumbly but will hold to together when squeezed).

Step 3

Divide dough into 2 pieces, making 1 piece about twice the size of the other. Flatten into 3/4" thick disks and wrap separately in plastic. Chill larger portion of dough in the freezer until hard, 30–35 minutes. Chill smaller portion of dough in the refrigerator until very firm, 40–45 minutes. Preheat oven to 350°. Chop remaining ¼ cup almonds and set aside.

Step 4

Once dough in freezer is hard, remove plastic and grate on the largest holes of a grater into pan. Using your fingers or a straight-sided measuring cup press about half of dough firmly up and around the sides of tart pan (or 1" high if you are using a springform pan), then press remaining dough firmly across bottom of pan.

Step 5

Spoon jam into center of crust and spread to the corners using an offset spatula or a spoon. Using your fingertips, crumble remaining disk of dough over the jam; sprinkle with reserved almonds, then 1 tbsp. demerara sugar. Chill tart in refrigerator until pastry is cold and firm, 25–30 minutes.

Step 6

Place tart on center rack in oven, then place a foil- or parchment-lined baking sheet on rack below and bake tart until jam is bubbling and pastry and almonds are deep golden brown, 45–50 minutes. Transfer tart pan to a wire rack and let tart cool in pan 30 minutes. Unmold and let cool completely. Serve tart with ice cream, if desired.

Step 7

DO AHEAD: Tart can be baked 1 day ahead.