You could buy a wavy one and have your SO cut off the entire horizontal part, leaving just a cone for you to use. Not sure what that does with the enamel so perhaps go for a blank aluminium form.
But you could probably achieve the same with a tall cupcake cup (ordinary cups can’t take the heat). Or two cups stacked for twice the height, one upside-up stacked on top of another that’s upside-down. Force them together if necessary with staples. You might need to cut out a smaller part of each bottom circle for air circulation, but far from all because you need stability. Ugly, yet kinda neat because you probably already have everything.