This Cinnamon Cupcakes recipe should result in fairly flat cupcake tops. In general, you'll want to ensure that you're not over-mixing the batter and that you're not over-filling the cupcake liners. They should not be more than 2/3 full. If you're having issues, it could also help to check your oven temperature. If it's too hot or not hot enough, it could impact how your cupcakes come out.