Preheat oven to 325 degrees.
In food processor with knife blade attached, pulse flour and sugar until combined. Add butter and pulse until dough begins to come together. Place dough in a large bowl. With hand, gently knead in nonpareils or sprinkles until evenly blended and dough forms a ball.
On lightly floured waxed paper, pat dough into 2 equally sized rectangles; freeze 20 minutes. Cut dough into 1-inch squares. Place squares, 1/2 inch apart, on an ungreased large cookie sheet.
Bake cookies 18 to 20 minutes or until lightly browned on bottom. Transfer cookies to wire rack to cool.
Store cookies in tightly covered container at room temperature up to 1 week, or in freezer up to 3 months.