Preheat oven to 350°F (177°C). Spray a 9 x 5 inch loaf pan with baking spray or grease and flour or grease and flour the loaf pan. To grease and flour, rub softened butter all over the surface of the inside of the pan and then add a couple tablespoons of flour. Tilt and tap the pan on all side until every greased surface is coated with flour. Set pan aside.
Sift flour, baking powder, baking soda, cinnamon and salt into a large bowl. Set aside.
Add buttermilk, bananas, eggs, butter, and dark brown sugar to a blender and blend for about a minute.
Pour wet ingredients into dry and stir to combine.
Stir in raisins until well distributed.
Pour batter into loaf pan and bake in preheated oven for 50-60 minutes. Bread is done with a toothpick or fork inserted into the center of the loaf comes out clean.
Allow loaf to cool in the pan on a wire rack for about 20 minutes. Remove loaf from pan and allow to cool completely. Once cool, slice into 9 one-inch slices.