Preheat oven to 350 degrees and line an 8x8" baking pan with parchment paper or lightly grease it with baking spray.
In a large mixing bowl, stir together melted butter and brown sugar until smooth and glossy.
Whisk in egg, egg yolk, and vanilla extract until combined.
Stir in flour, nonfat milk powder (if using), salt, and baking powder until just combined.
Fold in ¾ cup chopped Mini Eggs.
Spread batter evenly in the prepared pan and sprinkle and gently press remaining ¼ cup chopped Mini Eggs onto the surface of the blondie batter.
Bake for 22-26 minutes, until the edges are set and lightly golden, but the center still looks slightly soft.
Let blondies cool completely in pan before moving to cutting board and slicing.