1) Preheat oven to 350F with rack in middle. Blend together butter, sugars, vanilla, and 3/4 tsp salt in a bowl with a fork. Stir in flour and nuts (dough will be sticky).Form level tablespoons of dough into balls (total of 4

2) and arrange 2 inches apart on 2 ungreased large baking sheets. Flatten balls to 1/3 inch thick using bottom of a glass dipped in flour.

3) Bake, 1 sheet at a time, until edges are golden, about 20 minutes. Cool cookies on sheets 5 minutes, then transfer to racks to cool completely.Spoon 1 tsp jam onto flat sides of 20 cookies, then sandwich with remaining cookies. Dust with confectioner's sugar.