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Creamy Caramelized Onion Mashed Potato Bake
Sweet, jammy onions and nutty Gruyère cheese transform ordinary spuds into a rich, baked casserole. You'll love how the warm buttermilk and melted butter create an incredibly creamy base that contrasts with the savory mix-ins. It bakes up with a light, golden-brown crust while the center stays perfectly soft and fluffy. This is a fantastic side dish for holiday gatherings or a cozy weekend dinner when you're craving something extra special.
Ingredients
- 4 lb. russet potatoes, peeled and cut into 2-inch pieces
- 3 tsp. salt, divided
- 1¼ cups buttermilk, warmed
- ½ cup milk, warmed
- ¼ cup butter, melted
- ½ tsp. freshly ground black pepper
- 5 oz. Gruyère cheese, shredded (1¼ cups)
- 1 cup chopped caramelized onions
- 2 Tbsp. chopped fresh parsley
Instructions
- 1Heat the oven to 350°F. Place the peeled and cut potatoes in a large Dutch oven, cover them with water, and add 2 teaspoons of the salt. Bring the pot to a boil over medium-high heat and cook for about 20 minutes until the potatoes are tender, then drain.
- 2Return the drained potatoes to the Dutch oven and reduce the heat to low. Cook for 3 to 5 minutes, stirring occasionally, until the potatoes are completely dry. Removing excess moisture prevents a watery casserole.
- 3Mash the dried potatoes to your preferred consistency. Pour in the warm buttermilk, warm milk, melted butter, black pepper, and the remaining 1 teaspoon of salt. Mix gently just until everything is combined.
- 4Fold the shredded Gruyère cheese, chopped caramelized onions, and fresh parsley into the potato mixture. Transfer the blend into a lightly greased 2.5-quart baking dish or divide it evenly among eight 10-ounce ramekins.
- 5Bake for about 35 minutes until the top develops a light golden-brown crust.
Notes
- Prep: To make your own caramelized onions, cook thinly sliced yellow or sweet onions in a mix of oil and butter over medium-low heat for about 45 minutes. Once they turn deep golden brown, deglaze the pan with a splash of water, broth, or dry white wine.
- Make ahead: You can assemble the casserole up to a day in advance. Cover tightly and refrigerate, then add 10 to 15 minutes to the baking time.
- Storage: Keep leftovers in an airtight container in the fridge for up to 4 days. Reheat gently in the oven or microwave.