Combine and sift flour, salt, sugar and baking powder. Add butter, egg, and vanilla. Blend thoroughly, using hands. Place on lightly floured board. Divide into 4 equal parts. Shape each into a roll about 13 inches long and 3/4 inches thick. Place on ungreased baking sheet 4 inches apart and 2 inches from edge of sheet. Make depression 1/4 to 1/3 inches deep down center of each strip with knife handle. Fill depression with any kind of jelly you desire. Bake at 350 degrees for 15 to 20 minutes until light brown. While warm, cut diagonally into bars.