01 -
Preheat oven to 350°F (177°C). Generously grease an 8 x 8 x 2 inch square pan or a 9 x 2 inch round pan with butter or nonstick spray.
02 -
Evenly distribute 2/3 cup packed brown sugar over the bottom of the prepared pan. Scatter 4.5 tablespoons unsalted butter pieces over the sugar. Place pan in oven for 5 to 7 minutes, until butter is melted.
03 -
Remove pan from oven. Stir together melted butter and brown sugar to combine and spread evenly across the pan. Arrange banana slices to cover the bottom in a single layer. Set aside.
04 -
In a medium bowl, whisk together all-purpose flour, whole wheat flour, baking powder, baking soda, cinnamon, and salt. Set aside.
05 -
In a large bowl, beat 1/3 cup softened butter with 3/4 cup granulated sugar until creamy. Add eggs and vanilla extract and mix until well blended.
06 -
Mix in Greek yogurt (or sour cream) and mashed bananas until incorporated.
07 -
On low speed, add the flour mixture to the wet ingredients. Mix just until combined to avoid overmixing.
08 -
Pour the batter over the banana layer and gently smooth the surface. Bake at 350°F (177°C) for 30 minutes, then reduce oven temperature to 325°F (163°C) and continue baking for 25 to 35 minutes or until a toothpick inserted in the center comes out clean.
09 -
Allow cake to cool in the pan completely, or until the bottom is barely warm. Loosen edges with a knife, place a plate upside-down over the pan, and carefully invert cake onto the plate.