Preheat oven to 375°. In a large bowl, cream butter and sugar until light and fluffy. Beat in egg, milk and vanilla. In another bowl, whisk flour, baking powder and cinnamon; gradually beat into creamed mixture.
Using a cookie press fitted with a disk, press dough 1 in. apart onto ungreased baking sheets. Sprinkle with sprinkles. Bake 6-8 minutes or until set (do not brown). Remove from pans to wire racks to cool completely.
Spread about 1 teaspoon Biscoff on the bottoms of half of the cookies; top with remaining cookies.
Freeze option: Transfer dough to a resealable plastic freezer bag; freeze. To use, thaw dough in refrigerator overnight or until soft enough to press. Prepare and bake cookies as directed.