Preheat the oven to 350°F. Butter a 9 x 5-inch loaf pan and line with parchment paper so it hangs over the long sides of the tin. Set aside.
In a standing mixer fitted with a paddle attachment, cream together the butter and sugar until pale. Add the beaten eggs and sour cream and mix until well combined. Mix in the flour and baking powder until completely incorporated. Finally, add the mashed banana and ginger and stir to combine.
Pour into the loaf pan and bake in the oven for about 50-60 minutes, or until a toothpick inserted in the center comes out clean. Cool on a wire rack and slice to serve.