Preheat the oven to 375º and grease a cast-iron skillet with butter or cooking spray.
Set aside. In a large bowl, cream together the butter and sugar until it's light and fluffy, approximately 3-5 minutes.
8 oz butter, 50 grams cane sugar, 150 grams dark or light brown sugar
Crack in the eggs and whisk to combine. Pour in the vanilla and whisk again.
2 large eggs, 1 tablespoon vanilla extract or paste
To the wet ingredients, pour in the flour, baking soda, and salt. Fold in with a spatula until half of the batter is formed.
300 grams all purpose flour, 1 teaspoon baking soda
Crush the chocolate pretzels and add to the batter, and pour in the m&ms, and peanut butter pieces. Continue to fold in the ingredients until fully combined.
1 cup chocolate covered pretzels, ½ cup M&MS, ½ cup chocolate peanut butter pieces
Once the batter is formed, pour into the pre-greased cast-iron skillet. Push the batter flat and around the entire surface of the cast-iron skillet, making sure there is an even distribution.
Top with extra chocolate chips and m&ms. Bake for 30 minutes. Once done, let rest for 5-10 minutes before serving.