Sift first 4 ingredients; set aside.
Cream butter and sugar with electric mixer fitted with paddle attachment on medium speed until light and fluffy. Add eggs, 1 at a time, beating well after each. Mix in water until blended. Add dry ingredients all at once. Mix on low speed until incorporated, scraping side of bowl once.
Using #40 scoop, portion 0.75 oz. batter into each of 50 paper-lined mini muffin pans. Sprinkle with OREO Pieces.
Bake in 350°F standard oven 18 to 20 min. or until wooden pick inserted in centers comes out clean. Cool completely on wire racks.