Cut potatoes into 2 inch pieces and boil in heavily salted water, covered. About 12 minutes or until fork tender.
In a skillet melt the butter over medium low heat. Add the sage leaves and garlic, turn heat to a simmer. Cook until butter turns a golden brown and the aroma is nutty, about 4-5 minutes. Remove from heat, set aside.
In a large bowl mash the drained potatoes with the milk, Greek yogurt, salt and black pepper or add all to a mixer with paddle attachment to beat for a minute. Drizzle in half of the brown butter, reserving remainder and crispy sage leaves for later.
Mash until desired consistency, taste for seasoning and serve topped with remaining brown butter and crispy sage leaves.
Notes
If you do not have fresh sage leaves, after browning the butter with the garlic add 1/8 tsp of ground sage.