Rinse potatoes and boil in salted water for 15 to 20 minutes until fork-tender.

Meanwhile, melt the butter in a medium light-colored skillet over medium heat. Add sage leaves, smashed garlic, and thyme sprigs. Stir occasionally and watch closely. After 5 to 7 minutes, the butter will foam, then turn golden brown and smell intensely nutty. Remove from the heat, immediately lift out sage leaves with tongs, and set aside to crisp. Reserve 2 tablespoons of the brown butter in a small dish and set aside.

Drain potatoes and transfer them back to the warm pot for a couple of minutes to steam off excess moisture.

Warm buttermilk and cream in the microwave together for 45 to 60 seconds.

Mash the potatoes in the warm pot using a potato masher. Slowly pour in the brown butter, including the garlic and thyme pieces for flavor. Add the warm buttermilk and cream, a little at a time, stirring gently. Mix in the Parmesan cheese until the potatoes reach your desired creaminess.

If potatoes seem too thick, stir in a bit more warm milk or cream. Taste in season with salt and cracked black pepper.

Transfer to a serving dish. Drizzle the reserved browned butter on top and garnish with the crispy sage leaves. Serve immediately while hot.