Heat oven to 350°F (325°F for dark or nonstick pan). Spray 24 mini muffin cups with cooking spray. In medium bowl, beat butter and 3 tablespoons granulated sugar with electric mixer on medium speed until well mixed. Beat in 1 cup flour until dough forms.
Shape dough into 3/4-inch balls. Press 1 ball in bottom and up side of each muffin cup for crust. Bake 14 to 16 minutes or until edges begin to turn golden brown.
Meanwhile, in same bowl, beat remaining ingredients except powdered sugar on medium speed until well mixed.
Spoon 1 heaping tablespoon mixture evenly into each baked crust. Bake 10 to 12 minutes or until filling is light golden. Cool in pan 15 minutes. Remove from muffin cups to cooling racks. Cool completely, about 30 minutes.
Sift powdered sugar over tops of cookies. Store covered in refrigerator. If desired, sift additional powdered sugar over cookies just before serving.