1. Heat the oven to 350°. Grease the bottom and sides of a 9-by-3-inch loaf pan with butter, then dust with flour.
2. In a bowl, sft together the 13/4 cups flour, cinnamon, baking soda and salt. In another bowl, mash the bananas with the lemon juice.
3. In a large bowl, using an electric mixer, beat the 1 stick of butter with the sugar and vanilla. Beat in the eggs, one at a time. Add a third of the dry ingredients and half of the buttermilk; mix. Repeat until all of the dry ingredients and buttermilk are incorporated, then beat in the banana mixture.
4. Pour the mixture into the loaf pan and bake in the middle of the oven for 60 to 70 minutes, until the top of the bread is golden brown and a toothpick inserted in the center comes out clean. Let the bread cool in the pan for 10 minutes, then turn out onto a rack and let it cool completely.