01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - Whisk together flour, baking powder, and salt in a bowl. Set aside.
03 - Combine melted butter and brown sugar in a large mixing bowl. Mix until smooth.
04 - Beat in egg and vanilla extract until fully incorporated.
05 - Gently fold dry ingredients into wet mixture with a spatula until just combined. Do not overmix.
06 - Fold in white chocolate chips, milk chocolate chips, and chopped Cadbury Mini Eggs.
07 - Spread batter evenly into prepared pan. Press reserved whole Mini Eggs lightly onto surface.
08 - Bake for 22-25 minutes until top is golden and a toothpick inserted in center comes out with moist crumbs.
09 - Cool completely in pan. Lift out using parchment paper and cut into 12 squares.