Sweet Potato and Caramelized Onion Gratin

Prep 45 min
Total 1 hr 30 min
Servings 10

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If a family fight broke out over the last bite of this dish, we wouldn’t be at all surprised. When sweet potatoes are layered with caramelized onions and Parmesan cheese, then bathed in cream and baked to bubbly, golden perfection, the results are that good.

Ingredients

2 tablespoons butter
3 medium onions, cut into 1/4-inch slices
1 3/4 teaspoons salt
1 tablespoon balsamic vinegar
3 cups heavy whipping cream
2 sprigs fresh thyme
2 sprigs fresh sage
2 cloves garlic, crushed
1/2 teaspoon ground black pepper
2 1/2 lb (1.13 kg) sweet potatoes, peeled, cut into 1/4-inch slices
1 lb (500 g) Yukon Gold potatoes, peeled, cut into 1/4-inch slices
2/3 cup grated Parmesan cheese

Steps

1

1. Heat oven to 375°F. Spray 3-quart baking dish with cooking spray.
2

2. In 12-inch skillet, heat butter over medium-high heat. Add onions and salt; cook 15 to 20 minutes, stirring frequently, until onions are dark golden brown. Add balsamic vinegar; cook and stir 1 to 2 minutes or until onions are dark brown.
3

3. In 5-quart Dutch oven, add whipping cream, thyme, sage, garlic and pepper. Heat to boiling over medium heat. Remove from heat; let stand 10 minutes. Remove thyme, sage and garlic. Return heat to medium; add sweet potatoes and Yukon Gold potatoes. Cook and stir about 5 minutes or until potatoes are hot.
4

4. Spread one-third of the onions in baking dish. Layer half of the potato mixture, another one-third of the onions and 1/3 cup of the Parmesan cheese. Repeat with remaining potato mixture and onions. Drizzle any remaining cream over onions, and sprinkle remaining 1/3 cup Parmesan cheese over top. Cover with foil; bake 15 minutes. Remove foil; bake 25 to 30 minutes or until potatoes are tender and browned and bubbly. Remove from oven; let stand 15 minutes before serving.

Make sure to get the red-skinned, orange-fleshed sweet potatoes for this dish. They tend to be a bit sweeter and contrast nicely with the Yukon Golds.
Resist the urge to use half-and-half or milk in place of the heavy whipping cream, as it tends to break and result in a sauce with a curdled appearance.