Beat butter and cream cheese at medium speed with a heavy-duty electric stand mixer until creamy. Gradually add flour to butter mixture, beating at low speed just until blended. Shape dough into 72 (3/4-inch) balls, and place on a baking sheet; cover and chill 1 hour.
Place dough balls in cups of lightly greased miniature muffin pans; press dough to top of cups, forming shells.
Bake at 400° for 10 to 12 minutes. Remove from pans to wire racks, and cool completely (about 15 minutes).
Test Kitchen Tip: Baked pastry shells may be made up to 1 month ahead and frozen in an airtight container. Thaw at room temperature before filling.