In a food processor, process almonds until ground; set aside. In a large bowl, cream butter and 1/2 cup sugar until light and fluffy. Beat in egg and extract. Combine flour and salt; gradually add to creamed mixture and mix well. Stir in the ground almonds.
Divide dough in half; cover and refrigerate for 2 hours or until easy to handle.
On a lightly floured surface, roll out each portion of dough into a 12-in. x 9-in. rectangle. Cut lengthwise into three strips; cut each strip widthwise into six pieces. With a 3/4-in. round cutter, cut out a circle in the center of half of the pieces (discard circles).
Place 1 in. apart on ungreased baking sheets. Bake at 375° for 8-10 minutes or until golden brown. Remove to wire racks to cool completely.
For glaze, combine lemon juice and remaining sugar; thinly spread over whole cookies. Top with cutout cookies; fill center with 1/2 teaspoon jam.