You have a number of options for fixing cupcakes that sank in the middle, depending on the length of time the cupcakes have been out of the oven and the time you have before you need to serve these cupcakes. You can also learn how to avoid this problem in the future, which will help you feel confident in your baking skills.
Things You'll Need
If You Just Took the Cupcakes Out of the Oven
Insert a toothpick into the cupcake near the center to see if it comes out dry, with a few crumbs or with batter on it. If the toothpick does not come out clean, return the cupcakes to the oven to bake longer.
Make sure the oven is still at 350 F. Check every two to three minutes to see if the cupcakes are rising or if a toothpick comes out clean.
Remove the cupcakes from the oven when the toothpick comes out clean. If this has not solved the problem, go to the next section.
If the Cupcakes Are Fully Cooked
Prepare enough frosting to cover 1 1/2 the amount of cupcakes you have.
Add extra frosting to each cupcake to cover the depression and add a mound, as if it had risen normally.
Decorate with alternating colored icing or candied sprinkles, nuts or powdered sugar.
Avoiding This Problem in the Future
Get an oven thermometer to make certain your oven reaches the right temperature before placing the cake batter in the oven.
Avoid getting too much air into the batter if you are making a cake from scratch. That can happen three ways: using too much sugar; using too much baking powder or overbeating the eggs/butter/sugar mixture before you add the flour.
Do not open the door or make loud noises that cause the gas in the batter to escape.
Press your finger lightly in the center of the cupcake. Doing so should produce a springy feeling. If it does not spring right back, it is not yet done.