Going off this manga itd likely be like this:
Minos/Holstaurus milk base cheese.
Purified water brought into dungeon or filtered yourself.
Tomatos for sauce and peppers grown on the back of a Mud Golem
Meat from either a porcine or poultry based dungeon monsters like cockatrice or wild boars.
Living mushrooms for mushroom toppings.
Flour, salt, and yeast brought into dungeon or traded/bought/stolen from another party or dungeon resident.
Baking might be tougher so it may have to be over an open flame.
So not so much a specific monster as a variety of things required.

They baked a pizza on the dragon's stomach after Senshi exploded it. (Chapter 28 Red Dragon VI)