Preheat oven to 350°F. Line an 8x8-inch baking sheet with a parchment paper sling. Place Cadbury mini eggs in a ziploc bag and pound with a rolling pin a few times to break them up.
Place butter in a small saucepan and cook over medium heat, stirring frequently, until brown bits appear at the bottom of the pan, about 4-5 minutes. The butter will melt, then foam first, then start to smell nutty and you will notice that it is browning. Be careful because the butter can go from browned to burnt quickly, so don't leave the stove during this process. Remove the pan from the heat and let the browned butter cool for 5 minutes.
¾ cup salted butter
Add browned butter, brown sugar, and granulated sugar to a large mixing bowl. Beat with a hand mixer until combined.
1 cup light brown sugar, ¼ cup granulated sugar
Add eggs and vanilla extract. Beat again for 2-3 minutes until lightened and fairly thick.
2 large eggs, 1 teaspoon pure vanilla extract
Add flour, baking powder, and salt. Mix on medium-low speed just until combined.
1 ½ cups all-purpose flour, ¾ teaspoon baking powder, ½ teaspoon salt
Stir in crushed Cadbury mini eggs and chocolate chips. Transfer the batter to the prepared pan and spread in an even layer.
1 cup Cadbury Mini Eggs, ½ cup semisweet chocolate chips
Bake for 30-35 minutes until golden brown on top. Cool completely before slicing into squares.