Cream together the butter, sugar, and vanilla. Beat in the egg. Add lemon juice and lemon zest, mixing well.
Sift dry ingredients together; then add to creamed mixture. Mix well.
Drop by teaspoon onto ungreased cookie sheet, forming a round cookie with each teaspoonful of dough. Press thumb into each cookie center, making sure sides of cookie are rounded up around the thumbprint. Add a dab of raspberry jam to thumbprint of each cookie.
Bake at 350° for about 10-12 minutes, or until bottom edge of cookie begins to turn golden. Cool cookies on wire rack. If desired, sprinkle cookies with just a light sprinkling of powdered sugar.