Preheat oven to 325. Cream butter until soft, then gradually beat in sugar and egg until mixture is fluffy. Combine flour and baking powder; stir into butter mixture. Add vanilla and sesame seeds and mix well. Drop dough by teaspoonfuls onto greased cookie sheets, about 1- half inch apart. Bake 12-15 minutes, until cookies are light brown. Let cookies rest a minute, then remove immediately from baking sheet. If cookies harden before removal, return to oven for a minute to soften. "These cookies can be frozen, or will keep well in tightly-covered container." Recipe by Marian Burros, NY Times food columnist and author of severan cookbooks.