Cupcakes are tricky. Too little batter and you get a tiny treat. Too much and the cup overflows, creating a sticky mess and a look that’s less than attractive. Most recipes work best with cups filled two-thirds to three-quarters of the way full. If you’re in doubt, aim low. You can always pile on more frosting to make a short cupcake look taller, but there’s no easy fix for ones that have overflowed.