Marry Me Potato Gratin

Preheat the Oven:
Set your oven to 350°F (180°C). Lightly grease a 9x13-inch baking dish and set it aside.

Sauté Garlic and Tomatoes:
In a large saucepan over medium heat, melt the butter. Add the chopped sun-dried tomatoes and garlic, stirring for about 1 minute until fragrant.

Thicken with Flour:
Sprinkle the flour over the mixture and stir constantly for 1–2 minutes until it forms a light roux and takes on a slightly golden color.

Add Liquids and Simmer:
Slowly pour in the chicken broth, whisking to avoid lumps. Add the heavy cream, and bring the mixture to a gentle simmer while whisking. Let it cook for about 3 minutes, until slightly thickened.

Incorporate Cheeses and Seasonings:
Remove the pan from heat. Stir in the mozzarella, Parmesan, tomato paste, oregano, salt, and crushed red pepper. Mix until the cheese melts and the sauce is smooth.

Layer the Gratin:
Spread 1 cup of the sauce in the bottom of the baking dish. Add a layer of potato slices (about one-third of the total). Repeat two more times with the remaining potatoes and sauce, ending with sauce on top.

Bake Covered:
Cover the dish tightly with aluminum foil and bake for 1 hour 30 minutes to 1 hour 45 minutes, or until the potatoes are fork-tender.

Finish Uncovered:
Remove the foil and return the dish to the oven. Bake uncovered for another 20 to 25 minutes, or until the top is bubbly and golden brown.

Cool Before Serving:
Let the gratin rest at room temperature for 20 minutes before serving. This helps the dish set and enhances the flavor.