Since potions are basically a class of enchanted items, I would make the "double lore" rule count for them as well. That means a potion, even by invoking aspects, may not exceed double the casters lore. (YS280)
If you want more powerful potions, I'd make a thaumaturgy ritual out of it, only instead of directly casting the spell, you bottle it up for later use. If you can reasonably justify the spell you want to turn into a potion, I have no objections.
Keep in mind, that "potion" in the narrative sense and "potion" in the mechanical sense are 2 different things. In the mechanical sense, any 1 use item is called a potion, like Harry's sunlight handkerchief.