Melt the butter in a jug or bowl in the microwave in 10 seconds bursts. Use a cover as it will splutter.
Carefully chop half the Mini Eggs into pieces, and leave the other half whole.
In a large mixing bowl using a hand mixer or cake mixer, beat the melted butter, brown sugar, and caster sugar until light and fluffy - around 5 minutes.
Add the egg and vanilla essence and continue mixing until smooth.
Then add the flour, bicarbonate of soda, baking powder, and salt. Mix well to form a cookie dough. It will be quite stiff now.
Add the Mini Eggs and chocolate chips and mix thoroughly so they are evenly distributed throughout the dough.
Using a tablespoon, scoop the cookie dough out and using your hands, gently form uniform balls.
Put them on a flat baking tray and pop them in the freezer for 20 minutes or in the fridge for an hour until they firm up.
Preheat the oven to 180c.
Once the dough is chilled, space the balls evenly put on a lined baking tray. You may need to do these in batches as the cookies will spread out quite a lot. So try not to put them too close together or they will join.
Bake for 12 minutes until they're slightly golden and take them out of the oven. Let the cookies cool and harden slightly, before carefully transferring them to a wire rack to cool completely.
Serve and enjoy!