Before you begin, let the butter soften. Let eggs and yogurt come to room temperature. Preheat the oven to 350ºF with rack in the middle. Butter a 9-inch springform pan on the bottom and around the sides. Meanwhile, cut the peaches in half and remove the pit (seed). Slice 1 peach into 1/4 inch slices, then chop into 1/2 inch chunks. Set aside. Slice the other 2 peaches into 1/4 inch slices.