Preheat your oven to 350°F (175°C) and prepare a large baking sheet by lining it with parchment paper.
In a large mixing bowl, add the salted butter, dark brown sugar, and granulated sugar. Beat until light and fluffy, about 3 to 5 minutes.
Crack the eggs and additional yolk into the bowl, mixing well after each addition.
Gradually sift in the flour, baking soda, baking powder, and kosher salt, mixing on low speed until just combined. Fold in the oats.
Gently mix in the M&M’s, crushed pretzels, chocolate chips, and white chocolate chips until evenly distributed.
Roll the dough into ¼ cup-sized balls and place them about 3 inches apart on the baking sheet.
Bake for about 8 minutes, then rotate the pan and bake for an additional 2 minutes.
Press a few extra M&M’s on top and return to the oven for another 2 to 3 minutes.
Remove from the oven and allow to cool on the sheet for 5 to 10 minutes.
