Melt 1 cup of unsalted butter in a small saucepan over medium heat. Allow it to cool at room temperature for about 20 minutes.

In a large mixing bowl, whisk together 2 ½ cups all-purpose flour, 1 teaspoon baking powder, 1 teaspoon baking soda, and ½ teaspoon salt until lump-free.

In a separate bowl, mix the cooled melted butter with 1 cup dark brown sugar and ½ cup white granulated sugar until smooth. Add 2 large eggs and 2 teaspoons vanilla extract, beating until fluffy.

Gradually stir the dry ingredients into the wet mixture until just combined; avoid overmixing.

Fold in 1 cup M&M's, 1 cup white chocolate chips, 1 cup crushed pretzels, and any extra treats you prefer.

Using a 1½ oz ice cream scoop, portion out the dough onto a parchment-lined baking sheet, spacing them about 2 inches apart.

Refrigerate the dough for at least 1 hour or freeze for about 30 minutes.

Preheat the oven to 350°F (175°C).

Bake six dough balls at a time for 13–15 minutes, rotating halfway through for even browning.

Let the cookies cool on the baking sheet for about 5 minutes and decorate with extra M&M's or holiday sprinkles if desired.