For an extra touch of flavor, add a pinch of nutmeg or cardamom to the cinnamon sugar mixture. If you don't have muffin tins, you can bake the rolls on a parchment-lined baking sheet, but they may spread out more. Store leftover cinnamon rolls in an airtight container at room temperature for up to 2 days, or in the refrigerator for up to 4 days. Reheat gently in the microwave or oven before serving. Feel free to substitute other toppings, such as chopped nuts or dried fruit, for the chocolate chips.