Cream together butter and confectioners' sugar until light and fluffy. Beat in egg and vanilla. Mix in flour, salt, and poppy seeds until well blended. Drop dough from a teaspoon onto an ungreased cookie sheet. Make an indention in the middle of each cookie with your finger. If the dough is too sticky, dip your finger in water first. Fill each hole with about 1/2 teaspoon of cherry preserves.
Bake in preheated oven for 20 to 25 minutes, or until edges begin to brown.
