Preheat your oven to 375°F (190°C). Grease or line a 9x13-inch baking sheet with parchment paper.
In a large bowl, whisk together pancake mix, milk, eggs, vanilla, melted butter, and cinnamon until smooth.
Pour batter into the prepared baking sheet, spreading evenly.
Sprinkle your choice of mix-ins over the batter.
Bake for 15–18 minutes, or until golden brown and a toothpick inserted in the center comes out clean.
Let cool slightly, then slice into squares and serve with syrup or toppings of your choice.