Spray to coat an 8 1/2 x 4 1/2-inch loaf pan with cooking spray. In a large bowl, cream butter. Gradually add in sugar to form a smooth mixture; add the eggs, one at a time, beating well after each addition. Add bananas, yogurt, and vanilla; beat until just combined.
In a separate bowl, sift together flour, baking soda and salt; add to banana mixture; stir just until moist. Spoon batter into prepared pan. Bake for 1 hour or until a wooden pick inserted in center comes out clean. Cool 10 minutes in pan on a wire rack; remove from pan. Cool completely on wire rack.