### Scalloped Sweet Potatoes with Cheddar and Parmesan

**Recipe Description:**
Indulge in the creamy goodness of scalloped sweet potatoes, layered with sweet onions and a blend of sharp cheddar and Parmesan cheeses. This comforting dish is perfect for holiday gatherings or family dinners, offering a delightful twist on a classic favorite.

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**Ingredients:**
– 4 medium sweet potatoes, peeled and thinly sliced
– 1 medium onion, thinly sliced
– 2 cups heavy cream
– 1 cup shredded sharp cheddar cheese
– 1 cup grated Parmesan cheese
– 2 tablespoons unsalted butter
– 2 cloves garlic, minced
– 1 teaspoon fresh thyme leaves (or ½ teaspoon dried thyme)
– 1 teaspoon salt
– ½ teaspoon black pepper
– ½ teaspoon nutmeg (optional)
– 1 tablespoon olive oil
– Fresh parsley, chopped (for garnish)

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**Instructions:**
1. **Preheat Oven:** Preheat your oven to 375°F (190°C).
2. **Prepare Sweet Potatoes:** Peel and thinly slice the sweet potatoes (about 1/8 inch thick) using a mandoline slicer for uniformity.
3. **Slice Onion:** Thinly slice the onion.
4. **Make Cream Mixture:** In a medium saucepan over medium heat, melt the butter. Add the minced garlic and sauté for about 1 minute until fragrant. Pour in the heavy cream and stir in the thyme, salt, black pepper, and nutmeg (if using). Heat through without boiling.
5. **Add Cheese:** Remove from heat and stir in half of the cheddar and half of the Parmesan cheese until melted. Set aside.
6. **Layer Ingredients:** Grease a 9×13 inch baking dish with olive oil. Layer sweet potato slices, followed by onions, and pour a portion of the cream mixture over each layer. Repeat until all ingredients are used, finishing with cream on top.
7. **Top with Cheese:** Sprinkle the remaining cheddar and Parmesan cheese over the final layer.
8. **Bake Covered:** Cover the dish with aluminum foil and bake for 45 minutes.
9. **Bake Uncovered:** Remove the foil and bake for an additional 15-20 minutes, or until the top is golden brown and bubbly.
10. **Rest Before Serving:** Let the dish sit for 10-15 minutes before serving. Garnish with freshly chopped parsley.
11. **Serve:** Cut into squares or wedges and serve warm.

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**Notes:**
– For added heat, consider adding a pinch of cayenne pepper or diced jalapeños to the cream mixture.
– Experiment with different cheeses like Gruyère or fontina for varied flavors.
– This dish can be prepared ahead of time and refrigerated for up to 24 hours before baking. Add extra baking time if baking straight from the fridge.

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**Prep Time:** 20 minutes
**Cook Time:** 1 hour
**Total Time:** 1 hour 20 minutes
**Yield:** Serves 6-8 people

Enjoy this delicious and creamy scalloped sweet potato dish at your next gathering!