Brown the butter

• Optional step. Skip if not browning the butter, but be aware that using brown butter will yield the best results! In a small saucepan, brown the butter. When the butter is a golden amber color and gives off a nutty aroma, remove it from the heat and weigh it using a food scale. It should weigh about 198 grams (or the equivalent of 14 tablespoons). This is because some of it will evaporate when cooking. Place the butter in the fridge to cool for about 10-15 minutes before moving on. The butter can be warm, just not hot.
  16 tablespoons unsalted butter
• Once the brown butter is no longer hot, (it can be a bit warm) add brown sugar and white sugar to a large mixing bowl. Cream together with a hand mixer or in a stand mixer with the paddle attachment until light and fluffy, about 2–3 minutes. Be sure to scrape the sides of the bowl a few times to make sure everything is fully incorporated.
  1 cup brown sugar, ½ cup granulated white sugar, 14 tablespoons brown butter
• Next, mix in the egg, egg yolk, and vanilla extract. Mix until fully combined, but don’t continue to mix. Just make sure it’s totally combined with no streaks of egg or egg yolk.
  1 large egg, 1 large egg yolk, 1 tablespoon vanilla extract
• Sift in the flour, baking soda, and kosher salt. Mix gently to incorporate using a rubber spatula. When the dough is almost all of the way mixed (there may still be streaks of flour), fold in most of the chocolate chips, chunks, and crushed Cadbury egg pieces.
  1 ¾ cup + 2 tablespoons all purpose flour, 1 teaspoon baking soda, 1.5 teaspoons kosher salt, ⅓ cup semi sweet chocolate chips, ⅓ cup mini semi-sweet chocolate chips, ½ cup bittersweet chocolate chunks, 255 grams Cadbury eggs
• Scoop cookie dough using a large cookie scoop (#20 size) onto a parchment-lined baking sheet. Add some more chocolate chips, chunks, and whole Cadbury egg pieces to the top of the cookies. Chill the cookie dough balls for at least 30 minutes. You can also chill them for up to 2 days in the fridge or even freeze the dough balls (tightly wrapped) for up to 3 months if you plan to bake them later.
• After the cookies have chilled and it's time to bake the cookies, line a large cookie sheet with parchment paper and preheat the oven to 350°F. Once the oven reaches 350°F it’s ready to bake! Place about 5–6 cookies on the baking sheet, leaving lots of room between them.
• Bake for 13–15 minutes. The cookies are ready when the edges are golden brown, and the middle looks puffed, pale, slightly underdone, and a little gooey. The cookies will set up when they cool. Don’t overbake them.
• Sprinkle the cookies immediately with flaky salt while they are hot. Add on more Cadbury eggs and chocolate pieces if desired. Allow them to rest on the baking sheet for 3-5 minutes so they can firm up enough to move them. You can also use a round biscuit cutter to “scoot” the edges of the cookies while they are still hot and give them a nice round shape.
  Flakey salt
• Once the cookies have firmed up enough to move, transfer them to a wire rack to cool completely. Add the remaining balls of cookie dough to the baking sheet and bake those while the first round is cooling.
• Allow your baked cookies to cool and set up slightly before digging in, or else they will just fall apart. Once they have firmed up, enjoy!
• Store leftovers in an airtight container at room temperature for up to 5 days.