In a large bowl, cream butter and sugar until light and fluffy. Add eggs, one at a time, beating well after each addition. Beat in bananas. Combine flour and baking soda; add to creamed mixture just until moistened. Fold in pecans.
Fill greased or paper-lined muffin cups three-fourths full. Bake at 350° for 20-25 minutes or until a toothpick inserted in the center comes out clean. Cool for 5 minutes before removing from pans to wire racks.
As a substitute for each cup of self-rising flour, place 1-1/2 teaspoons baking powder and 1/2 teaspoon salt in a measuring cup. Add all-purpose flour to measure 1 cup.