Preheat your oven to 350°F. Lightly spray a 9x13" baking dish with nonstick spray, then pour in the melted salted butter and swirl to coat the bottom evenly. As a personal tip, I suggest ensuring the whole base is buttered to help the casserole release easily and add extra flavor.

Remove the cinnamon rolls from the two tubes, making sure to set aside the included frosting for later. Cut each cinnamon roll into pieces about 3/4" thick. Scatter all the cut pieces evenly into the prepared baking dish with melted butter.

In a bowl, whisk together the eggs, milk, maple syrup, vanilla extract, and ground cinnamon until smooth and well combined.

Pour the custard mixture from Step 3 evenly over the cinnamon roll pieces in the baking dish, ensuring all pieces are moistened. Bake in the preheated oven for 25–35 minutes, or until the top is lightly golden brown and the casserole is puffed and set.

Allow the casserole to cool for 10–15 minutes after baking. Then, drizzle the reserved package frosting over the top and serve warm. For an extra treat, I like to serve mine with a little extra maple syrup on the side.