DAY BEFORE: Cream butter and cream cheese together until smoothly blended. Beat in the flour. Shape dough into a smooth ball, wrap in foil or cling wrap, and refrigerate overnight or up to a week.
AT BAKING TIME: Remove dough from refrigerator 30 minutes before using. Start heating oven to 375 degrees F (190 degrees C).
Roll chilled dough thin. Cut with 3 or 4 inch round cookie cutter. Place small spoonful of jam in center of each round, moisten edges with water.
Fold round over and press edges together. Bake on ungreased cookie sheet 15 to 20 minutes. Immediately roll in sugar mixed with cinnamon (traditional) OR in confectioners' sugar if preferred.
