Potion making

[Minigiant]

When making potions, do you use up the spell prepared when it is made?

Or could I make 3 or 4 potions from preparing one spell?

[Pizza Lord]

You use up the slot, though you don't technically cast the spell.

Creating Potions wrote:

The act of brewing triggers the prepared spell, making it unavailable for casting until the character has rested and regained spells. (That is, that spell slot is expended from the caster’s currently prepared spells, just as if it had been cast.)

This isn't usually an issue, since you can only work on one magic item at a time and a potion takes one day to brew. If you did have a way to do so, then you would need to use an additional spell slot for each additional potion.

[Quixote]

You are, in essence, casting the spell into the item, where it is stored for later.