- 4 lb potatoes, peeled and diced (I prefer Yukon Gold)
- 2 teaspoons kosher salt, for cooking the potatoes
- 6 tablespoons unsalted butter
- ⅓ cup fresh sage leaves, plus more for garnish
- 4 oz mascarpone cheese, at room temperature
- 1 cup milk
- 1 cup grated mozzarella cheese
- 1 cup panko breadcrumbs
- Salt and pepper, to taste
- Preheat the oven to 400°F and butter a 2-QT baking dish.
- Place the potatoes in a large pot and fill with enough cold water so the potatoes are covered by at least an inch of water. Add 2 teaspoons of kosher salt to the pot.
- Bring the potatoes and water to a boil over medium-high heat and then cook for 12-15 minutes, or until they are very tender.
- While the potatoes are cooking, heat the butter in a small saucepan over medium heat. Once it is melted, add in the sage leaves. Reduce the heat to low and cook until the butter is bubbly and lightly brown and the sage leaves are crisp, about 5 minutes. Remove from the heat and set aside.
- Drain the potatoes and return them to the pot. Start mashing the potatoes with a potato masher.
- Pour in roughly 4 tablespoons of the sage butter (reserve the rest, along with the crispy sage leaves, for serving), the mascarpone cheese, and the milk.
- Keep mashing and stirring the mixture until the potatoes are fluffy and creamy and all of the ingredients have been well incorporated. Fold in the mozzarella cheese. Season the potatoes with salt and pepper, to taste.
- Transfer the potatoes to the prepared baking dish, smooth out the top, and then sprinkle on the panko breadcrumbs.
- Place the baking dish in the oven and bake, uncovered, for 15-20 minutes or until everything is bubbly and the top is golden brown.
- Remove, allow to cool slightly, and then serve hot. Drizzle the remaining sage butter over top just before serving. Garnish with the crispy sage leaves.