In large bowl, combine flour, oat bran, oats, raisins and baking powder. Pour in buttermilk and use large rubber spatula to combine well. If dough becomes too stiff to stir, flour hands and finish mixing by hand. Shape dough into round loaf 7-inches in diameter. Smooth top and sides. Line baking sheet with parchment paper and set loaf on it. Use sharp knife to slash an ?X? about 1/4-inch deep in top. If any raisins are visible, poke into dough with your fingers so they won?t burn. Sprinkle loaf with a bit of flour. Bake at 425° about 45 minutes, or until bottom of loaf sounds hollow when tapped. Let cool completely before slicing.