Preheat your oven to 375°F (190°C). Lightly grease a standard 9x13 inch baking dish with the tablespoon of butter or cooking spray.

Open the canned cinnamon rolls. Set the included icing packets aside for later use.

Place each cinnamon roll flat on a cutting board. Using a sharp knife or kitchen scissors, cut each roll into four equal pieces (quarter them).

Scatter the cut cinnamon roll pieces evenly across the bottom of the prepared 9x13 inch baking dish. The pieces should fill the pan and touch each other, but do not compress them too tightly.

In a large bowl, whisk together the 6 large eggs, 1/2 cup whole milk, 1/4 cup heavy cream, 1 teaspoon vanilla extract, and 1/2 teaspoon ground cinnamon. Whisk until the mixture is completely uniform, slightly frothy, and no streaks of egg yolk remain.

Carefully pour the liquid custard mixture evenly over the scattered cinnamon roll pieces in the baking dish. Ensure every piece is thoroughly covered and coated by the egg mixture.

Allow the bake to sit undisturbed for 5 to 10 minutes to allow the cinnamon rolls to fully absorb the liquid. This ensures a moist interior.

Place the baking dish into the preheated 375°F (190°C) oven. Bake for 28 to 32 minutes, or until the top is golden brown, the center is set, and a knife inserted near the center comes out clean.

Remove the French toast bake from the oven and place it on a wire rack.

Prepare the reserved icing packets. If the icing is too thick, place the sealed packets in a bowl of warm water for a few minutes or microwave them (unsealed, in a separate bowl) for 5 to 10 seconds to loosen the consistency.

Snip the corner of the icing packets and generously drizzle all the icing over the warm French toast bake. Serve immediately while warm.