Heat oven to 350 degrees. Grease and flour two 8-inch round cake pans. In a bowl, sift together flour, baking soda, baking powder, and salt. Set aside.
Cream together butter and sugar. Add egg yolks one at a time. In another bowl, mash bananas, and combine with buttermilk and vanilla. Add alternately to butter mixture with flour mixture, beginning and ending with flour.
Beat egg whites until stiff; fold into batter.
Divide batter between prepared pans. Bake until a toothpick inserted into the center comes out clean, 30 to 35 minutes. Let cool in pans for 5 minutes, then turn out onto a rack to cool completely.
When cake layers are cool, whip cream with confectionersâ€™ sugar until stiff. Fold in sour cream. Place a cake layer on a plate, and spread with filling to within 1 inch of edge. Place other layer on top, and press down lightly. Chill for 1 hour.
Slice bananas 1/2 inch thick. Melt butter in a large saute pan over medium heat. When it sizzles, add slices in a single layer. Sprinkle with sugar. When golden brown, turn slices; cook until brown on other side.
Carefully pour in bourbon (using a measuring cup, never the bottle) and ignite with a match. Cook until flames die down, shaking the pan to toss bananas in syrup. Remove from heat.
Arrange banana slices on top of cake. Pour remaining syrup over cake, letting it drip down sides. Serve immediately.