Preheat your oven to 350°F (175°C) and prepare an 8x8 inch baking pan by greasing it lightly with butter or lining it with parchment paper.

In a medium saucepan over low heat, melt ½ cup of unsalted butter until fully liquid, stirring gently to avoid scorching.

Mix in 1 cup of light brown sugar and ½ cup of granulated sugar once the butter is melted and off the heat, stirring until glossy.

Allow the mixture to cool slightly, then whisk in two large eggs one at a time, followed by 1 teaspoon of pure vanilla extract.

In a separate bowl, sift together 1 cup of all-purpose flour, ½ teaspoon of baking powder, and a pinch of salt, then fold into the wet ingredients.

Gently fold in 1 cup of chopped mini Cadbury eggs, distributing them evenly throughout the batter.

Pour the batter into the prepared pan, spread evenly, and bake for 25-30 minutes, or until edges are golden.

Remove from the oven and allow to cool in the pan for 10-15 minutes before cutting into squares and serving.