In a food processor, whirl almonds until finely ground.
In a bowl, with an electric mixer on high speed, beat butter and sugar until fluffy. Beat in egg and almond extract until well blended. Stir or beat in ground almonds and the flour.
If using tart pans (about 2 in. wide and 3/4 in. deep; you'll need about 4 dozen pans total--bake in sequence if necessary), press a 1 1/2-teaspoon portion of dough over bottom and up sides to rim of each pan (dough should be 1/4 inch thick). Set tart pans slightly apart in 10- by 15-inch baking pans (if baking in sequence, cover unused dough lightly with plastic wrap). Fill each tart with 1/4 teaspoon jam.
If not using tart pans, shape 1 1/2-teaspoon portions of dough into balls and set about 2 inches apart on 12- by 15-inch baking sheets (recipe fills three sheets). With the tip of your finger, make a 1/2-inch-wide, 1/2-inch-deep indentation in the center of each ball; fill each with about 1/4 teaspoon jam.
Bake in a 350° oven until tarts are golden brown, 16 to 18 minutes; switch pan positions halfway through baking. Cool about 10 minutes on pans or sheets. Invert tart pans one at a time to release tarts, and set upright on racks; or transfer cookies from baking sheets to racks to cool.