Found in witch huts in forest biomes, one for each hut.
A witch hut is comprised of two floors. The first floor has a cauldron and four minor healing potions placed around the fireplace. The hearth is not lit and has a hidden entry to the basement, which contains a chest and extra minor health potions. Like any other type of dungeon, witch huts reset every now and then, so witch huts can be used to obtain a decent number of minor potions without having to craft them.