Chocolate Chip Banana Muffins

Ingredients:

cooking spray
 3/4 cup white sugar
 6 tablespoons butter, softened
 6 tablespoons ground flax seed
 1 teaspoon vanilla extract
 2 eggs
 2 cups all-purpose flour (or 1 c ap flour and 1 c whole wheat flour)
 1 teaspoon salt
 1 teaspoon baking soda
 3 ripe bananas, mashed
 3/4 cup chocolate chips
 1/2 cup chopped walnuts (optional)

Directions:
Preheat oven to 350 degrees F. 
Spray muffin cups with cooking spray or line with paper liners.
Beat sugar, butter, flax seed, vanilla, and eggs together in a bowl with an electric mixer until smooth and creamy.
Sift flour, salt, and baking soda together in a separate bowl. 
Add flour, 1/2 cup at a time, into the butter mixture, until fully incorporated and batter is stiff. Beat bananas into batter with an electric mixer on low. 
Fold chocolate chips and walnuts into batter; spoon into the prepared muffin cups, filling each cup 3/4 full.
Bake in the preheated oven until a toothpick inserted in the center of a muffin comes out clean, about 25 minutes. Cool in the tins for 10 minutes before removing to cool completely on a wire rack.