Preheat the oven to 400° F. Line 3 baking sheets with parchment paper and set aside.
Slice the remaining cold butter (⅓ cup) into ¼ inch cubes and add them to the standing mixer. Add the brown sugar and cane sugar as well. Once the brown butter has re-solidified (90% is close enough), add it to the standing mixer. Mix on medium speed for about 3-4 minutes, until there aren't any chunks of butter left.
1 cup unsalted butter, ¾ cup light brown sugar, 1 cup cane sugar
While the butter and sugar are mixing, whisk together the flour, sea salt, cornstarch and baking soda in a separate bowl. Set aside.
2 ½ cup all purpose flour, 1 ½ teaspoon fine sea salt, 2 teaspoon cornstarch, 1 teaspoon baking soda
Add the eggs and vanilla extract to the standing mixer and mix on medium speed until creamy (2-3 minutes).
2 large eggs, 1 tablespoon vanilla extract
Crush ½ cup of Cadbury mini eggs into smaller pieces. I prefer to do this by putting them in a bag and crushing them with a rolling pin.
2 cup Cadbury mini eggs
Add the whisked dry ingredients to the standing mixer, and stir on lowest speed. As it mixes, add the semi-sweet chocolate chips, white chocolate chips, crushed Cadbury eggs, and 1 cup of whole Cadbury eggs. Only mix until the dry ingredients are just barely incorporated to avoid over-mixing.
¾ cup semi-sweet chocolate chips, 2 cup Cadbury mini eggs, ½ cup white chocolate chips