Line a baking tray with parchment paper or a silicone baking mat. Set the tray aside.
Add the butter, brown sugar and white sugar to a mixing bowl and whisk together.
3/4 cup melted butter, 3/4 cup dark brown sugar, 1/2 cup sugar
Add the egg and vanilla and whisk again.
2 eggs, 1 Tablespoon vanilla extract
Add the flour, baking soda, cornstarch and salt to the bowl and stir until the batter is thick and shiny.
2 1/4 cup flour, 1 teaspoon baking soda, 1 1/4 teaspoon cornstarch, 1/2 teaspoon salt
Keep the Cadbury eggs in the bag and hit them with a rolling pin or bowl to crush them into smaller pieces. Pour the broken eggs into the cookie dough and mix well.
1 bag (16 ounces) Cadbury Mini Eggs
Scoop the cookie dough into ¼ cup balls and place them on the prepared cookie tray, spacing them about 2-3 inches apart.
Place the tray in the fridge and let the cookie dough cool for at least an hour.
Preheat the oven to 325 degrees Fahrenheit.
Take the tray of cookie dough out of the fridge and place it right into the hot oven. Bake the cookies for 10 minutes. They will still look a little soft but the tops will no longer be shiny and wet and the edges of the cookies will be golden brown.
Let the cookies cool for 10 minutes on the tray and then enjoy.