Preheat oven to 350°F. Beat butter and miso with a heavy-duty electric stand mixer on medium speed until creamy; add brown sugar, and beat until light and fluffy. Add eggs, 1 at a time, beating just until blended after each addition. Add vanilla, and beat just until blended.
Stir together flour, baking powder, baking soda, salt, and nutmeg. Gradually add flour mixture to butter mixture, beating at low speed just until blended. Stir in bananas just until blended. Spoon batter into 2 lightly greased (with cooking spray) 8- x 4-inch loaf pans, filling three-fourths full.
Bake in preheated oven until a wooden pick inserted in center comes out clean, about 1 hour. Cool in pans on a wire rack 10 minutes. Remove from pans, and cool completely, about 30 minutes. Drizzle each loaf with Yuzu Glaze.