On the subject of Roses, Rose Levy Beranbaum has an interesting discussion on the addition of fat—either butter or oil—to a bread. Very small additions will lubricate the gluten and make a loaf expand; larger amounts will actually reduce the volume of loaf, making it heavy and dense.
For banana bread, I’m solidly in the heavy camp. The gold standard, as far as I’m concerned, is the loaf that emerges from the Kahaluu kitchen of a family friend. We were once brazen enough to ask for the recipe.
Mrs. Beachy, the infallibly gracious and generous baker, hesitated only for a second. “Of course I’ll give you the recipe,” she said, “I’m just a little sad–if I give you the recipe, I won’t be able to make you banana bread anymore–”
“—Please don’t give us the recipe!” I interrupted.
We must have taken it anyway, because it’s now on file. Vegetable oil reliably yields the extraordinarily smooth, dense, moist, heavy loaf we knew and loved. Wrapped in foil and chilled, it is almost more terrine than loaf. You could slice it with a piece of floss.
Rosie’s banana cake is something entirely different. It is exactly as heavy and banana-packed as our favorite bread, but has the tender crumb of butter and a crisp crust (I think the baker’s vocab is “lid”) under its icing.
We have a very thin friend who uses applesauce instead of butter or oil in her banana bread. It’s good, but has no place amidst buttercream clouds.