Preheat oven to 375 degrees. In a large bowl, combine the sugar and the egg and blend well. Add the mashed bananas, applesauce, and yogurt and stir to combine. Stir in the chocolate chips. In a separate bowl, combine the flour, baking powder, baking soda, and salt. Make a well in the center of the flour mixture and pour the wet ingredients into the well. Stir until just blended. The batter will be lumpy.
Pour the batter evenly into the two 8-cup muffin pans that have been well greased or lined with paper muffin cups. Bake for 10-15 minutes, or until a toothpick inserted in the center of a muffin comes out clean.
This is a light-colored muffin so be careful not to overbake. Let the muffins cool in the pan for 2-3 minutes, then carefully remove and place on a wire rack to cool.
NOTE: You can substitute two 4-oz jars of banana baby food (such as Gerber) for the applesauce and use just 1 ripe banana. Or try other baby food fruits such as pineapple, apple or plum.