Preheat oven to 350°F. Grease a 9-inch square baking pan OR an 8-inch square baking pan.
Melt the butter and chocolate chunks in a small saucepan on low heat. Stir constantly until melted. Remove from heat and cool for 5 minutes.
In a large mixing bowl, beat sugar, vanilla and eggs on medium high speed until combined and smooth, about 2 minutes. Pour in chocolate and beat on low until combined. Beat in flour on low speed until blended. Stir in Mini Eggs.
Spread brownie mixture into baking pan. Bake for 40 minutes. Remove from oven and cool on a wire rack for a couple hours
Chocolate Frosting
Melt butter and cocoa powder in the microwave in a large bowl.
Stir in milk and vanilla.
Add powdered sugar and beat on medium speed until smooth.