Preheat oven to 350F with the rack in the middle. Take 15 of the Mini Easter eggs and cut them in half. Set the remaining 3 aside. Spray a 9-inch glass pie dish with non-stick cooking spray.
Place the melted butter and cookie butter in a microwave-safe bowl and microwave for 30 seconds just until the Cookie Butter can be mixed to a smooth consistency with the butter. Set aside for 30 seconds to allow the mixture to cool. Add in the egg and mix until well combined. Add in the brown and granulated sugar and mix until smooth. Add the flour and salt, and stir just until there are no traces of flour. Do not overmix and do not use a mixer.
Gently fold in 3/4’s of the chopped (mini peanut butter eggs). The cookie dough will have almost a thicker consistency. Just fold in gently.
Place the dough into the prepared pie dish, gently pressing down to make level. Take the remaining 1/4 chopped peanut butter eggs and gently push them down into the dough just so they are flush with the top of the dough. Sprinkle coarse sanding sugar on top.
Bake for about 26-28 or until a toothpick inserted in the center comes out mostly clean, or with a few moist crumbs. Remove the cookie pie from the oven and place on a cooling rack.
Allow the pie to cool in the dish for at least 30 minutes before slicing and serving. The pie will have crisper edges with a soft center. If you prefer a crispier cookie all the way through, cook for a few more minutes. While the pie is cooling take the remaining 3 Easter eggs (non-cut) and garnish on top in the middle for decoration.