Ago Perrone's recipe, good for 23 oz: Warm 10 oz of butter until brown, then mix with 23 oz of bourbon and simmer without bringing to a boil. Remove from the 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. Strain through a fine cloth. Pour the resulting bourbon back into the bottle.