Preheat the oven to 350°F (175°C) and prepare a 12-inch round pizza pan by greasing it or lining it with parchment paper.

In a large bowl, cream the butter, brown sugar, and granulated sugar until light and fluffy. Beat in the eggs one at a time, then add the vanilla extract.

In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, mixing until just combined.

Fold in the M&M’s, chocolate chips, and sprinkles until evenly distributed in the dough.

Press the dough evenly into the prepared pan. Bake for 20–25 minutes until the edges are golden and the center is set.

Allow the cookie cake to cool completely in the pan. Decorate with frosting, candy eyeballs, or additional sprinkles as desired before slicing and serving.