Instructions

• Preheat oven to 350°F. Line a 15×10" rimmed sheet pan with parchment paper leaving a 1–2" overhang on two opposite sides for easy removal; lightly spray the parchment with non-stick spray.
• In a large bowl, using a mixer, cream together 1 cup unsalted butter (at room temperature), 1 cup light brown sugar (packed), and 3/4 cup granulated sugar for about 1 minute, until light and combined.
• Add 2 large eggs and 2 teaspoons vanilla extract to the butter mixture and mix just until combined.
• In a separate bowl, whisk together 3 cups all-purpose flour, 1 teaspoon baking soda, and 3/4 teaspoon salt.
• Add the dry ingredients to the wet ingredients and stir with a spatula or mixer on low just until the dough comes together. Do not overmix.
• Divide the dough into 4 equal portions (by weight or visually) and place each portion into its own medium bowl.
• Add the mix-ins to each bowl as follows, then gently fold each mix-in into its dough portion until evenly distributed: one bowl — 1/2 cup M&M's; second bowl — 1/4 cup sprinkles; third bowl — 1/4 cup white chocolate chips and 1/4 cup dried cranberries; fourth bowl — 1/4 cup chopped peppermint bark and 1/4 cup chocolate chips.
• If you want extra visible mix-ins on top, reserve a few pieces from each mix-in before folding them in and set them aside.
• Transfer each flavored dough portion to one quadrant of the prepared sheet pan. Using an offset spatula or the back of a spoon, spread and flatten each portion evenly within its quadrant to form a uniform layer. Press reserved mix-ins on top if using.
• Bake in the preheated oven for 13–15 minutes, or until the tops are just barely golden brown.
• Remove the pan from the oven and place on a wire rack. Allow the cookie slab to cool completely in the pan.
• Using the parchment overhang, lift the cooled slab onto a cutting board. For each quadrant, cut into 6 pieces by making 3 even lengthwise slices across the quadrant and then cutting each slice in half (3 × 2 = 6 per quadrant), yielding 24 pieces total.