Combine flour, baking soda, salt, sugar, buttermilk, egg, vanilla and peanut butter into a large mixing bowl. Stir until thoroughly mixed. Add the diced banana and gently stir into the batter.
Spoon about 1/4 c. of batter into a non-stick skillet over medium heat. With spoon, form a round pancake. Let cook until batter starts to bubble, takes about 1-2 minutes. Flip and cook until browned, about 1-2 additional minutes. Transfer to plate.
Continue until all pancake batter is used. Keep pancakes warm.
For the Syrup
Combine butter, sugar and milk into a medium saucepan over medium heat. Stir until melted. When mixture starts to boil reduce heat and stir in baking soda and vanilla. Syrup will bubble and rise. Remove from heat and stir in Nutella until melted. Drizzle over pancakes.