Preheat your oven to 350°F. Line rimmed baking sheets with unbleached parchment paper and set them aside.
In a small bowl, place the flour, xanthan gum, baking soda, and salt, and whisk to combine well. Set the bowl aside.
Set aside 14 of the Cadbury mini eggs. Place the remaining candies on a flat surface and apply even pressure with the heel of your palm as gently as possible to break each egg in half. Place the pieces in a small bowl and refrigerate to chill while you make the cookie dough.
Place the granulated sugar, brown sugar and butter in the bowl of a stand mixer fitted with the paddle attachment (or a large mixing bowl with a handheld mixer handy), and beat for about 5 minutes or until light and fluffy. If your butter was on the colder side, beat for longer.
To the butter and sugars mixture, add the egg yolks and vanilla, and beat until fully combined.
Add the dry ingredients to the mixing bowl, and mix on low speed (or by hand) until everything is absorbed, creating a thick but soft cookie dough.
Add the chilled mini egg pieces. Mix by hand using a mixing spoon or spatula until they’re evenly distributed throughout the cookie dough.
Using a medium-size ice cream scoop or two spoons, place rounded portions of the dough (each about 2 tablespoonsful) on the prepared baking sheet, about 2-inches apart. Top each with one whole mini egg, pressing the egg down gently to help it adhere to the raw cookie dough. Do not flatten the mounds of dough.
For thicker cookies, chill the portions in the refrigerator for 10 minutes. This step is totally optional.
Place the baking sheet in the center of the preheated oven and bake until the cookies are lightly golden brown around the edges and set in the center, about 15 minutes. They should not glisten or appear wet in the center.
Remove from the oven and allow to cool on the baking sheet until firm, about 10 minutes.
Notes
For the flour blend.My favorite gluten free flour blends are Better Batter's original blend gluten free flour and Nicole's Best multipurpose blend. Bob's Red Mill 1-to-1 Gluten Free Baking Flour should also work, but you'll need to add an additional 1/2 teaspoon xanthan gum to your dry ingredients or the cookies will look good, but will be crumbly.Cup4Cup changed its formula and doesn't seem to work as well as it has in the past, so I don't recommend it. To make your own blend using one of my “mock” recipes, please see the all purpose gluten free flour blends page.For the butter.To bring your butter to cool room temperature, which is about 68-70°F, cut it into large chunks (no more than 1 tablespoon each) and let it sit at room temperature for about 30 minutes (longer if your kitchen is colder). It should give a bit when you press it with your finger, but should not be warm or greasy.For dairy-free, use good quality vegan butter and replace the Cadbury eggs with dairy free chocolate chips. For the egg yolks.To bring eggs rapidly to room temperature, place them in a bowl of very warm (not hot) water for about 15 minutes. Then, crack them and separate out the yolks.For slightly cakier cookies, use 1 whole egg instead of 2 egg yolks.For egg free, try 1 "chia egg" or "flax egg" in place of 2 yolks.