Preheat the oven to 180°C / 160°C fan.
In a large bowl whisk together the melted butter, brown sugar and caster sugar until smooth.
Add the egg and vanilla and whisk again until thick and glossy.
Stir in the flour, baking powder, bicarbonate of soda until a soft cookie dough forms.
Fold through the crushed Mini Eggs and chocolate chips.
Press the dough into a 20 ovenproof frying pan or small baking dish, spreading it out evenly. Scatter a few extra Mini Eggs over the top.
Bake for 18–22 minutes until the edges are golden but the centre is still soft.
Leave it to cool for 5 minutes, then serve warm straight from the pan with scoops of vanilla ice cream.