Preheat oven 180C/350F/Gas 4 and line a brownie tin with baking paper or parchment paper
Melt to butter in the microwave or in a bowl over a pan of water. Leave to cool for a couple of minutes.
In a large bowl, mix the melted butter with the cocoa powder and caster sugar.
Add the eggs, flour and chocolate chips to the melted chocolate mixture and mix well.
Fold in most of the Cadburys Mini Eggs, reserving a few for the top.
Pour the brownie batter into the prepared tin and smooth into an evenly layer.
Bake in the oven for 15 minutes before removing and adding the remaining Mini Eggs to the top of the bake.
Put back in the oven for another 10-15 minutes until the brownie is starting to brown and coming away from the tin around the edges. It should still be slightly soft in the middle.
Leave to cool completely in the tin and then slice and enjoy.