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