Preheat oven to 350Â°F degrees. Spray an 8x8 baking pan or 9-inch pie plate with cooking spray.
In a small microwaveable bowl, combine raisins and bourbon (or rum or apple juice â€“ whatever youâ€™re using). Stir. Nuke 60 seconds. Set aside.
In a mixing bowl, combine flours, cinnamon, baking powder, baking soda, nutmeg, and salt. Stir to combine.
To a separate bowl or stand mixer, mix brown sugar and butter on medium speed until well combined. Add banana, milk, vanilla, and eggs. Mix until combined. Slowly add dry ingredients until all are just incorporated into a wet batter. Stir in raisins and nuts. Pour into baking pan.
Bake 30 minutes. Remove and cool fully on a wire rack. Dust with powdered sugar, if desired.