Brown the butter. In a small skillet over medium heat, add butter. Using a silicone spatula, occasionally scrape sides and bottom of pan until butter is melted, has a slightly nutty smell and turns golden in color. Be careful to not burn the butter, it can happen quickly if not paying attention. Transfer butter to a large bowl and allow to cool.

After a few minutes when the butter is slightly cooled, stir in the bananas, sweetener, yogurt, eggs and vanilla until well mixed. Add the flour and stir just until combined, being careful to not overmix the batter.

Add half the batter to the prepared pan and carefully spread into an even layer. Using a spoon, drop have the chocolate hazelnut spread in several mounds over the batter. Using a fork or toothpick, swirl it into the batter.

Add the remaining batter to the loaf pan and spread into an even layer. Repeat dropping the remaining chocolate hazelnut spread by spoonful over the top and swirl into the batter.

Bake the bread until golden brown and a toothpick inserted in the center comes out clean, about 50-60 minutes.

Remove from oven and place pan on a wire rack to cool for about 10 minutes, then remove the bread from the pan and place it directly on the wire rack to cool completely.