Preheat the oven to 180C/350F/Gas 4, and line a baking tray with parchment paper or a silicone mat. Set aside.
Whisk together the flour, baking powder, baking soda, cornflour, and salt. Set aside.
In a separate large bowl, whisk together the butter and sugars. Add the egg and vanilla, and mix until combined.
Add the dry ingredients and mix until just combined. Fold in the chocolate chips and Mini Eggs.
Roll the dough into 2-oz balls (or use a medium cookie scoop), and place onto the prepared baking tray. Bake for 10 - 12 minutes.
Allow to cool on the baking tray for 5 - 10 minutes before transferring them to a wire rack to cool completely.
Video
Notes
Cookies stay fresh, kept in an airtight container, at room temperature for up to 1 week.Cookie dough balls can be kept in the fridge for up to 5 days, or frozen for up to 3 months. Bake straight from frozen.