In a mixing bowl, mash the large ripe banana until smooth. Add the egg, melted butter or oil, and pure vanilla extract. Whisk until fully combined. Gradually add in the milk, mixing well.
In a separate bowl, whisk together the self-raising flour, granulated sweetener, baking powder, and a pinch of salt. Slowly incorporate the dry ingredients into the wet mixture, stirring until just combined.
In a microwave-safe bowl, melt 3/4 cup of Nutella until smooth. This will be used to stuff the pancakes.
Heat your non-stick skillet or griddle over medium heat. Once hot, pour a ladleful of pancake batter onto the skillet. Let it cook for about 2-3 minutes until bubbles start to form on the surface.
Before flipping, spoon a small amount of the melted Nutella onto the center of the pancake. Pour a bit more batter over the Nutella to cover it.
Carefully flip the pancake and cook for another 2-3 minutes until golden brown. Repeat until all the batter is used.
In a small bowl, mix the remaining 1/4 cup of Nutella with 1-2 tablespoons of milk to create a drizzle. Stack the pancakes high, drizzle with Nutella, and serve warm.