Ago Perrone, recipe sufficient for 700 ml: Warm 300 g of butter until brown, mix with 700 ml of bourbon and bring to a simmer, but not to boil. Remove from heat, cover with cling wrap and leave to infuse for at least an hour. Pour into a metal container and store in the freezer. When the oil is fully hardened and risen to the surface, peel it off. Fine strain through the cloth. Pour ready bourbon back in the bottle.