Add 1 stick of butter to a skillet set over medium heat. Cook until the butter begins to brown, about 3-4 minutes. Remove from the heat and transfer to a heatproof bowl. Freeze for 10-15 minutes, but no longer.
Preheat the oven to 350° F. Line a baking sheet with parchment paper.
In a bowl, beat together the remaining stick of butter, the cooled browned butter, and the brown sugar until combined. Beat in the eggs and egg yolk, one at a time, until combined. Add the vanilla, beating until creamy. Add the flour, baking soda, and salt.
Fold in 1 1/4 cups of the M&M's, pretzels, chocolate chips, and chocolate chunks.
Mix the sugar and cinnamon in a bowl. Roll the dough into rounded 2-3 tablespoon-size balls and then roll through the cinnamon sugar. Place 3 inches apart on the prepared baking sheet.
Bake for 8 minutes, then rotate the pan and push the remaining M&M's into the cookies. Bake for 2-3 minutes more. Remove from the oven and let the cookies cool on the baking sheet. They will continue to cook slightly as they sit on the baking sheet.
Eat warm or let cool and store in an airtight container for up to 4 days.
