Preheat the oven to 410 and line two baking sheets with silicone mats or parchment paper.
Carefully chop the Cadbury mini eggs in to big chunks or put them in a bag and use a rolling pin to gently smash them
In your mixer bowl cream together the cold, cubed butter and both sugars for approximately 3 minutes.
Beat in the eggs, one at a time, scraping down the sides in between, then add the vanilla.
In a separate bowl, whisk together the flour, cornstarch, baking soda and salt. Add it to the creamed butter, sugar and egg mixture and mix until just combined.
Mix in the chocolate chips then stir in the egg pieces, (minus the reserved.)
Using a large cookie scoop, separate the dough in to 12 equal size balls of dough, yes they are HUGE.
Place six balls of dough on each cookie tray. Bake for 10-12 minutes until the cookies are light golden brown on the top.
As soon as you remove the cookies from the oven, gently push in the pieces of eggs that you reserved – If you push down using the jagged edge they will pop through that beautiful crispy outer edge easier.
Let the cookies sit on the trays for 10 minutes, then transfer the cookies to the cooling racks. Let cool at least another 10 minutes before eating so they set.