Begin by melting 1/4 cup of butter. Then, pour 2 tablespoons of the melted butter into an 8-cup bundt pan, ensuring you brush it evenly over the pan's sides and bottom. In a separate bowl, combine brown sugar, cinnamon, nutmeg, and almonds. Sprinkle half of this mixture onto the bottom of the pan and reserve the remaining mixture, which you will later combine with the remaining melted butter.
Start by combining 1/4 cup of butter with granulated sugar in a large bowl. Gradually incorporate the eggs, one at a time, until fully blended. Finish by adding the orange peel and banana for a harmonious mixture.
Mix together all-purpose and whole-wheat flours, baking powder, soda, and salt. Then, add this mixture to the banana mixture along with the buttermilk, stirring until everything is well blended.
Begin by pouring half of the batter into the prepared pan. Next, evenly spoon the remaining brown sugar mixture over the top, and finish by covering it with the remaining batter.
Bake at 350°F until a skewer comes out clean, about 50 minutes. Cool on a rack for 5 minutes, then invert onto a plate. Serve warm or cool.