How small? You could make teeny rings from foil covered card or use small round biscuit cutters. If you did them in a bun tin, I reckon they wouldn't turn out unless you froze them in the tin and turned them out frozen.....maybe line the bun tin with cupcake papers?
you can buy pastry rings, so will produce a flat base, but I would go with making a large base, cutting out with pastry cutters, and then adding the topping before fridging them, should be fine.........
I would make a large one in a rectangular/square dish, once its set, pop it in the freezer for 20 mins before cutting out the size/shape you require ( just to save the topping from warming up)
Don't know if you have a Morrisons near to you, but whilst in there today, I noticed in their First Home range, they had a 12 cup bun tray at 89p, I remembered this post and thought that they would be ideal. They weren't very deep but would take a mini cheesecake and would be easy to get out once made too.