Place the potatoes in a large pot, add water to cover by at least 1 inch and season with salt. Bring to a boil over medium-high heat; once boiling, reduce heat to medium. Let the potatoes cook for 12–15 minutes, until tender.

Meanwhile, in a small pot melt the butter over medium-high heat, and then let it cook and bubble until it starts to foam and smell like toasted nuts and caramel, about 5 minutes. Remove the pot from the heat. Set aside.

In a small non-stick pan, add 1⁄4 cup oil over medium-high heat. Once hot, add sage leaves, cooking for 15 seconds each side, until they have curled and crisped but not browned. Transfer to a paper towel-lined plate. Set aside.

Once the potatoes are tender, drain and add back to the pot. Mash potatoes, adding buttermilk, milk and browned butter, reserving 2 tbsp of butter. Season with salt to taste.

Transfer to a serving bowl and drizzle over remaining browned butter. Garnish with fried sage leaves and pepper.