Banana Bread

I know almost everyone has their own banana bread recipe, but here's a really great one I found online about a month ago. I love this recipe so much that I'm buying bananas to sit on the counter for a week just so I can make banana bread! It only calls for 1/3 cup butter, so the bread tastes really healthy. At least, that's what I like to think!!

Here's the recipe:

3 or 4 ripe bananas, smashed
1/3 cup melted butter
1 cup sugar (I use 3/4 brown sugar instead)
1 egg, beaten
1 teaspoon vanilla
1 teaspoon baking soda
Pinch of salt
1 1/2 cup of flour
1 teaspoon cinnamon (optional, this is my own addition!)

No need for a mixer for this recipe. Preheat the oven to 350°F. With a wooden spoon, mix butter into the mashed bananas in a large mixing bowl. Mix in the sugar, egg, and vanilla. Sprinkle the baking soda and salt over the mixture and mix in. Add the flour last, mix. Pour mixture into a buttered 4x8 inch loaf pan. Bake for 1 hour. Cool on a rack. Remove from pan and slice to serve.

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By the way, has anyone successfully tried substituting anything (such as yogurt or applesauce) for butter? What about substitutions (such as egg whites) for whole eggs? I always read about them, but I am always too scared to try.