1. Preheat the oven to 350˚F (175°C). Line a muffin pan with 12 paper liners.

2. Beat together the butter and brown sugar until light and fluffy. Add the eggs one at a time, beating well between each addition.

3. Sift together the flour, baking soda, baking powder, ground ginger, and salt. Add gradually to the butter mixture. Add the mashed banana, sour cream (or yogurt) and milk. Mix until everything is combined (don’t over mix).

4. Divide batter amongst 12 lined muffin cups, bake for 15-18 minutes until a toothpick inserted in center comes out clean. Cool completely before frosting.

5. For the buttercream: In a large bowl over simmering water whisk together the egg whites, sugar and salt. Continue whisking until the mixture is at a 160°F (71°C). Pour the mixture into the bowl of a stand mixer fitted with a whisk attachment. Beat for about 5 minutes until stiff peaks form and the mixture has cooled to room temperature.

6. Add the butter gradually, one tablespoon at a time. Add the vanilla extract and powdered sugar. Continue to beat for another 5 minutes until the mixture is creamy and all butter is incorporated. Frost cupcakes using an open star tip. Drizzle with melted chocolate (or sprinkle with chopped nuts) and let cool.