Cream together 3/4 lb butter or margarine, 1-1/4 c. sugar, 2 eggs, and 1 tsp. vanilla.
Blend in 3-3/4 c. flour and 1 tsp. salt.
Spread 3/4 of batter on an ungreased 10 x 15″ jellyroll pan. Spread 1 c. jam or fruit preserves over batter. Top with crumbles of remaining batter (you may need to add a little more flour to avoid sticking).
Bake at 350 for 35 minutes or until edges become light golden brown. Cool completely before cutting.