Preheat oven to 350 degrees Fahrenheit.
Grease and flour a nine inch by five inch loaf pan.
For the streusel: mix the flour and sugar, then cut in the cold butter until the mixture is crumbly. Set aside.
For the banana bread: whisk together the first five ingredients.
With a pastry blender or two knives, cut in the shortening until the mixture resembles coarse crumbs.
Stir in the bananas, eggs and vanilla until all ingredients are just combined. Do not over mix.
Spread 1/2 the batter into the prepared pan.
Spread 1/3 to 1/2 cup of Nutella over the batter. If the Nutella is hard to spread, place in microwave at 50% power for one minute.
Place the remaining batter over the Nutella, then sprinkle the prepared streusel topping over the batter.
Place in the oven for about 55 minutes. The bread is done when a cake tester inserted into the middle of the bread comes out clean, and the bread has started to pull away at the sides.