Melt 1 cup of butter with the muscovado (or brown) sugar over medium heat, stirring. Mix 1 teaspoon of vanilla into the melted butter/sugar mixture.
Grease a large round cake pan. Pour the butter/sugar caramel mixture into the cake pan and spread it evenly over the bottom. Arrange the bananas on top of the caramel mixture.
Now, it's time to make the cake batter. Beat the remaining butter with the granulated sugar until light and fluffy. Add the egg and remaining vanilla to the butter/sugar mixture. Stir in the flour, baking powder, ginger, and cinnamon. Add the sour cream to the cake batter and beat until smooth.
Pour the batter over the bananas and smooth it out.
Bake the cake for 1 hour, or until a skewer inserted into the middle comes out clean.
Let the cake cool in the pan for 15 minutes.
Flip the cake over onto a plate, slice, and serve.