*Cadbury egg tip: to chop them easily, place them in a sealed ziplock baggie, and give them a whack with a rolling pin to crush them up! If you attempt chopping them on a cutting board, it can get pretty messy so this is my preferred method.
Preheat and prep: Preheat the oven to 325°F. Spray a standard half sheet pan (13-inch x 18-inch) with nonstick spray and set aside. Whisk melted butter & sugars: Add the melted butter and sugars together in a large mixing bowl and whisk together until smooth. Be sure to break up any clumps of brown sugar (using fresh/soft brown sugar is best!)
1 cup unsalted butter, melted and slightly cooled, 1 1/2 cups dark brown sugar, packed, 1 cup granulated sugar
Add the rest of wet ingredients: pour in the eggs, egg yolks, milk, and vanilla extract. Whisk again until fully combined.
2 large eggs, room temperature, 2 large egg yolks, room temperature, 2 Tbsp. whole milk, 1 1/2 Tbsp. pure vanilla extract
Dry ingredients: add in the dry ingredients and fold until mostly combined.
3 1/2 cups all-purpose flour, spooned and leveled, 2 tsp. cornstarch, 1 tsp. baking soda, 1 tsp. baking powder, 1 1/2 tsp. kosher salt
Chocolate time: add in ~1 cup chopped Cadbury Egg pieces and chocolate chips. Fold into the batter. It will be quite thick, that's perfect.
3/4 cup chocolate chips, 9 oz. bag Cadbury eggs, chopped
Spread on baking sheet: Turn the batter out onto the prepared baking sheet. Spread evenly until smooth. Trust the process, it will all spread out and fit on the pan 🤗 Top with more Cadbury egg pieces and chocolate chips if desired, or you can sprinkle a few on top AFTER it bakes so they get melty on the tops post baking.
Bake: Bake for ~19-22 minutes. Ovens vary so keep an eye on them. I always underbake because there will be carry over cooking as it cools on the sheet pan. The cookies will look puffy at first, but settles as it cools. You can gently tap it on the counter if it’s really fluffy so it settles, if needed.
Cool & enjoy: Decorate the top with more chocolate if desired and flaky sea salt. Cool completely, cut into portions and enjoy!
garnish with more crushed Cadbury eggs, chocolate chips, and flaky sea salt