Preheat oven to 325 degrees
Spray 8x8 glass baking dish with cooking spray- set aside
Combine sugars, butter & vanilla in mixer & beat until combined
Stir in egg
Add flour - beat until well combined
Press 3/4 of the dough into prepared baking dish.
Place remaining dough in refrigerator until it's time to use it
Bake 20 minutes - remove & allow to cool about 15 minutes
Spread dulce de leche over the top in thin layer
Drop remaining dough in clumps on top of the dulce de leche - do not spread out or press down.
Return to oven & bake 25-30 minutes
Remove from oven & place on wire rack in pan.
Melt candy melts in small bowl for approx 1 minute to melt - stirring after 30 seconds
Take a fork & dip in melted chocolate & drizzle over the shortbread bars
Allow to cool completely before serving.