Good Morning..

My friend is getting married and wants banana cake. I have never made one so I did a trial run last night. I used this recipe...

Ingredients
2 tablespoons lemon juice
2/3 cup milk
2 large very ripe bananas, mashed
1 (18.25 ounce) package butter cake mix
1 teaspoon baking soda
1/2 cup butter, softened
3 eggs
1 teaspoon vanilla extract


The taste amazing, however all but 3 of the cupcakes sank in the middle. I followed this recipe exactly. The only difference was I had only 1/4 cup of butter so I used that plus I Cant believe its not butter to make up the difference. Would that cause this? Or maybe was my baking soda old?

I am not so worried with the cupcakes the icing will take care of that but I am worried about the cake.

TIA.

I had the same issue with the pumpkin cupcakes I recently made. I read that if you don't cook them long enough and they are still soft on the inside then they will sink. I baked my second batch 5 minutes longer and they came out great.