Step 1: Brown the Butter - Place the butter in a saucepan over medium heat. Stir constantly as it melts. The butter will foam and bubble for a few minutes before settling down. Keep stirring until the butter turns a warm amber color and small brown bits form at the bottom of the pan. The smell will be nutty and slightly caramel like. Remove from heat and let it cool for 15 to 20 minutes until warm but not hot.
Step 2: Cream the Butter and Sugars - In a large mixing bowl whisk the browned butter with the dark brown sugar and white sugar for about one minute. This helps dissolve the sugar and creates a smooth base for the dough. Add the eggs one at a time mixing well after each addition. Stir in the vanilla extract.
Step 3: Combine the Dry Ingredients - In a separate bowl whisk together the flour, baking soda, and baking powder. Gently fold the dry mixture into the wet ingredients until just combined. Try not to overmix since that can make the cookies tough.
Step 4: Add the Oats and Mix Ins - Fold in the rolled oats, chopped toasted pecans, and chocolate chips. Stir until everything is evenly distributed throughout the dough. The dough will be thick and rich.
Step 5: Chill the Dough - Cover the bowl and refrigerate the dough for at least one hour. Two hours will produce thicker cookies. Chilling is important because the browned butter is liquid and needs time to firm up again.
Step 6: Bake the Cookies - Preheat the oven to 350 degrees Fahrenheit or 175 degrees Celsius. Use two small scoops or about three tablespoons of dough per cookie and place them on a lined baking sheet. Bake for 11 to 13 minutes until the edges are golden brown and the centers still look slightly soft. Immediately press crushed Cadbury Mini Egg pieces on top of the warm cookies. If desired add a light sprinkle of flaky salt. Let the cookies cool slightly before serving.