Monster Cookies
4 1/2 cups (405g) quick cooking oats
2 teaspoons baking soda
1 1/2 cups (410 g) extra crunchy peanut butter
1/2 cup (113g) unsalted butter, softened
1 cup (200g) granulated white sugar
1 cup packed (210g) light brown sugar
3 large eggs
1 tablespoon vanilla extract
1 cup (170g) semi-sweet chocolate chips
1 cup (170g) M&M's, plus more for decorating

Double Doozie Filling
1 pound confectioners' sugar
1 tablespoon butter, softened
1/2 cup (100g) clear vegetable shortening, at room temperature
1/4 teaspoon salt
1/2 teaspoon vanilla extract
4 tablespoons milk, plus more if needed