In a medium bowl, mash the ripe banana with a fork until smooth but still slightly chunky for texture. Add the egg, melted butter or oil, milk, and vanilla extract. Whisk together until well combined.
In a separate bowl, sift together the self-raising flour, baking powder, salt, and granulated sweetener.
Gradually add the dry ingredients into the wet banana mixture, stirring gently until just combined. Avoid overmixing to keep pancakes fluffy.
In a small bowl, melt 3/4 cup of Nutella gently in the microwave for 15-20 seconds or until pourable. Add 1-2 tablespoons of milk to loosen, stirring until smooth. Carefully fold about 1/3 of the pancake batter into the melted Nutella, creating a marbled effect when combined with the rest of the plain batter.
Place your non-stick pan or griddle over medium heat. Lightly grease with butter or oil to prevent sticking.
Spoon about 2 tablespoons of plain batter onto the pan, spreading it slightly into a circle. Add a dollop (about 1 tablespoon) of the 1/4 cup Nutella in the center, then cover with another 2 tablespoons of the marbled Nutella batter to seal the filling inside. Cook for 2-3 minutes until bubbles form on the surface and the edges look set.
Carefully flip the pancake and cook for another 1-2 minutes until golden brown and cooked through. Repeat with remaining batter and Nutella filling.
Serve your Nutella Stuffed Banana Pancakes warm with extra Nutella drizzled on top, fresh banana slices, or a dusting of powdered sugar for a stunning presentation.