Preheat the oven to 350°F (175°C) and grease a baking pan.
Combine the melted butter and brown sugar in a mixing bowl, stirring until smooth.
Add the egg and vanilla extract, mixing well until fully incorporated.
Whisk together the flour, baking powder, and salt in a separate bowl.
Gradually add the dry ingredients to the wet ingredients, stirring until just combined.
Fold in the mini chocolate eggs gently into the batter.
Pour the batter into the prepared baking pan and spread it evenly with a spatula.
Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted in the center comes out clean.
Allow to cool in the pan before cutting into squares.