1. Preheat your oven to 350° F. Make sure your baking sheet is lined with parchment paper, which will prevent the cookies from sticking and make cleanup a breeze.
2. In a large mixing bowl, combine the butter, brown sugar, and granulated sugar. Beat them together until you achieve a smooth and creamy mixture. The color should change to a lighter shade, indicating that air has been incorporated.
3. Add the eggs and the additional egg yolk, one at a time, mixing well after each addition. This ensures everything is well combined and contributes to that lovely texture.
4. Now, it’s time to scoop in the flour, baking soda, baking powder, and salt. Beat these dry ingredients into the wet mixture until just combined. Be careful not to overmix!
5. Fold in the old-fashioned oats gently using a spatula. This will add the chewy texture that we love.
6. Next, it’s time to mix in the fun stuff! Add the M&M's, crushed pretzel sticks, chocolate chips, and white chocolate chips. Gently fold these in until evenly distributed.
7. Using your hands or a cookie scoop, roll the dough into balls about 1/4 cup in size. Place the dough balls on the prepared baking sheet, making sure to leave 3 inches of space between them.
8. Transfer the baking sheet to the preheated oven and bake for 8 minutes. After this time, rotate the pan to ensure even baking and bake for an additional 2 minutes. The cookies should be lightly golden.
9. Remove the pan from the oven, and immediately push a few extra M&M's into the top of each cookie. Return to the oven for an additional 2 to 3 minutes. This will give you that lovely, warm, and gooey center!
10. Once baked, let the cookies cool on the baking sheet for a few minutes. They will continue to cook slightly as they sit. I recommend eating at least one warm for the best experience!
