Mix milk, granulated sugar and yeast in large mixing bowl. Whisk in eggs, butter and vanilla until well blended.
Combine flour and salt in separate bowl. Make a well in the center. Pour in milk mixture. Mix until soft dough is formed. Cover dough with oiled plastic wrap. Let stand at room temperature to proof 30 min. or until doubled in volume. Gently fold in pearl sugar.
Line a full sheet pan with parchment paper; spray with cooking spray. Use #20 scoop to portion 10 dough balls evenly spaced in 2 rows, leaving several inches between each. Spread each ball to a 6x4-inch oval.
Sprinkle half the ovals each with 2 Tbsp. OREO Base Cake. Using the parchment, carefully lift second oval and place over Base Cake to form 5 waffle "sandwiches." Refrigerate at least 30 min. or until firm.
When ready to cook, carefully remove top parchment paper. Place waffle in preheated Belgian waffle maker and cook according to manufacturer's directions.