In a large bowl beat butter and sugar until creamy; beat in egg yolk, vanilla, and lemon peel. In another bowl, stir together flour and salt. Gradually add to butter mixture, blending thoroughly. Shape dough into ropes about 3/4 inch in diameter and as long as your baking sheets; place them about 2 inches apart on ungreased baking sheets. With the side of your little finger, press a long groove down the center of each rope (don”t press all the way down to baking sheets). Bake cookies in a 375 degree oven for 10 minutes. Remove cookies from oven and spoon jam into the grooves. Return to oven for 5-10 minutes or until cookies are firm to touch and light golden brown. While cookies are hot, drizzle them with powdered sugar mixture (or spread mixture along sides of cookies). Then cut at a 45 degree angle into 1 inch lengths. Let cool briefly on baking sheets; transfer to racks and let cool completely. Store airtight. Makes about 4 dozen.
