1. Preheat oven to 350°. Sift together first 4 ingredients in a large bowl. Mash bananas with lemon juice in a small bowl. (You want a little texture—like semi-lumpy mashed potatoes.)
2. Beat butter and next 3 ingredients at low speed with a heavy-duty electric stand mixer 1 minute or until combined. Increase speed to medium, and beat 1 1/2 to 2 minutes or until light and fluffy. Add eggs, 1 at a time, beating until blended after each addition, stopping to scrape bowl as needed.
3. Add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture. Beat at low speed just until blended after each addition. Add banana mixture, beating just until batter is blended (no more than 10 seconds). Pour batter into a well-buttered and floured 8- x 4-inch loaf pan, and place on a baking sheet.
4. Bake at 350° for 55 to 60 minutes or until a long wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 minutes. Remove from pan to a wire rack, and cool 50 minutes. Wrap in plastic wrap (it will still be warm—this helps the bread stay moist), and store at room temperature up to 4 days.