Season duck breast with salt & pepper on both sides and sauté over high heat, about 3 minutes on each side. Turn heat to low, cover, continue to cook until golden brown, about 5 minutes. The insides should still be pink. Remove from pan and keep warm. Microwave peach halves on high for 2 minutes and keep warm while you finish the sauce. Add stock to pan and place over medium-high heat, scraping up the browned bits. Stir Peach Schnapps into the stock and continue stirring until mixture comes to a boil. Remove pan from heat and whisk in cold butter all at once. Slice duck breasts on the diagonal. Place a peach half on each of 4 heated plates. Fan the slices of duck breast on the plate next to the peaches. Spoon a little of the sauce over the duck and peaches. Serve, passing the remaining sauce separately at the table.