By Grocery List Plus Editorial Staff | Published on October 4, 2026
Serves 8
398 cal · 390 min
Fresh Tomato Au Gratin
Recipe GLPR31e8397a980cc0
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Average rating: 3.8 (1)
A rich and savory layered casserole featuring fresh plum tomatoes with a creamy sauce, Swiss cheese, and a crispy panko topping. The tomatoes are salted and drained for hours beforehand to concentrate their flavor and prevent a watery dish. Perfect as an elegant side dish for any meal.
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Ingredients
3 pounds plum tomatoes such as Roma, cut into large chunks
2 teaspoons kosher salt for draining tomatoes
3 tablespoons melted butter
2 cups chopped onions
1 tablespoon minced garlic
2 tablespoons all-purpose flour
1 ½ cups heavy cream
½ teaspoon kosher salt
¼ teaspoon white pepper
½ teaspoon dry Colman's mustard
½ teaspoon freshly grated nutmeg
A few drops Tabasco sauce
8 ounces Swiss cheese, shredded and divided
½ cup fresh basil, chopped
1 ½ cups panko bread crumbs
½ teaspoon paprika
Directions
Prepare the tomatoes 4 to 6 hours in advance or overnight: Place the cut tomato chunks in a colander set over a bowl. Sprinkle generously with the 2 teaspoons of salt for draining and toss to coat evenly. Allow the tomatoes to sit and release their liquid, stirring gently and occasionally pressing down with a large spoon or small flat bowl—do not mash them aggressively. Continue this process for several hours until the tomatoes are well drained. Pat dry with paper towels if needed to remove excess moisture.
Preheat the oven to 375°F.
In a medium pot, melt the 3 tablespoons of butter over medium-high heat. Add the chopped onions and minced garlic, then sauté for 3 minutes until fragrant and beginning to soften.
Reduce heat to medium, sprinkle the flour over the onion mixture, and stir frequently for 3 minutes to cook out the raw flour taste.
Microwave the heavy cream until it is hot but not scalding—this prevents lumps when you add it to the flour mixture.
Pour the hot cream into the onion and flour mixture while whisking constantly to combine smoothly.
Add the ½ teaspoon kosher salt, white pepper, dry mustard, nutmeg, and a few drops of Tabasco sauce. Stir well to combine all seasonings, then remove from heat.
Spray the inside of a 9-inch round, 3-inch deep casserole dish with cooking spray. Ladle approximately 1/3 cup of the cream sauce onto the bottom of the dish to coat it lightly.
Layer the casserole as follows: half of the drained tomatoes, half of the remaining cream sauce, half of the shredded Swiss cheese, all of the chopped fresh basil, the remaining tomatoes, the remaining Swiss cheese, and finally the rest of the cream sauce.
In a small bowl, combine the panko bread crumbs, 3 tablespoons melted butter, and paprika. Mix until the crumbs are evenly coated with butter and paprika, then sprinkle this mixture evenly over the top of the casserole.
Bake uncovered for 30 minutes until the top is golden brown and the edges are bubbling.
Remove from the oven and let the casserole rest for 15 minutes before serving. This allows the layers to set and makes for cleaner portions.
Comments
This au gratin works year-round at Charlotte chains, but the 390-minute time is misleading: most of that is passive drying or resting, yet the active prep and assembly still run 45-60 minutes on a weeknight when you factor in slicing, salting, sautéing the aromatics, building the sauce, and layering. A pound of fresh tomatoes (the anchor ingredient) will cost $2–3 at Harris Teeter or Food Lion in winter and under $2 midsummer, putting the dish at roughly $1.75–2.50 per serving once you add butter, cream, and cheese. The real caveat is execution: salting tomatoes to draw moisture and then managing that liquid through baking requires attention, and the dish is best eaten fresh from the oven—leftovers are watery and lose texture. This is a thoughtful side or light supper for a patient cook who can plan ahead, not a weeknight grab.
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