In a small saucepan, heat the cream over medium heat. Peel and lightly crush the garlic clove so it splits open and add to the cream. Add 5-6 sage leaves to the cream. Bring the cream to a gentle simmer then cover and remove from the heat. Let steep while the potatoes cook.
Peel the potatoes and cut into chunks. Add to a large pot of water and place over high heat. Bring the water to a boil and cook until the potatoes are fork tender. Drain the potatoes and transfer back to the pot.
Remove the garlic clove and sage leaves from the cream. Add the cream to the potatoes along with the kosher salt and pepper and mash until smooth.
In a small skillet or saucepan, melt the butter over medium heat. Let the butter simmer gently until it begins to brown, about 4 to 5 minutes. The butter will foam and then become clear, with the milk solids dropping to the bottom of the pan. Swirl the pan while the butter is cooking to make sure it browns evenly.
When the milk solids in the butter turn brown, add the remaining sage leaves and swirl for another few seconds. Remove from the heat.
To serve, spoon one third of the mashed potatoes into a serving dish and drizzle with one third of the brown butter and sage leaves. Repeat two more times finishing with the remaining brown butter. Enjoy!