Step 1

Preheat oven to 300 degrees F (150 degrees C). Grease 4 loaf pans, 7x3-inch size. Combine 1 tablespoon white sugar with 2 teaspoons cinnamon in a small bowl. Dust the insides of the greased loaf pans with the cinnamon sugar.

Step 2

Stir whole wheat flour, oats, all-purpose flour, baking soda, 1 1/2 teaspoon cinnamon, and salt in a bowl. Beat 2 cups brown sugar with 3/4 cup butter in a separate mixing bowl until creamy. Beat in sour cream, bananas, eggs, and vanilla extract until smooth. Stir the dry ingredients into the banana mixture and fold in 2 cups dates, 1 cup walnuts, and 1/2 cup toasted coconut.

Step 3

Spoon the batter into the prepared loaf pans. Sprinkle tops of each loaf with about 1 tablespoon of dark brown sugar and 1 1/2 teaspoons each of dates, walnuts, and coconut. Brush each loaf with melted butter for a shiny glaze.

Step 4

Bake loaves in the preheated oven until browned and a toothpick inserted into the center of a loaf comes out clean, about 1 hour.