Preheat oven to 350 F degrees. Spray a 9x5 baking loaf pan with nonstick spray and set aside.
In a bowl sift together all purpose flour, cinnamon powder, salt and baking soda. Set aside.
Start making the brown butter. Take 1 stick of unsalted butter and add it to a pan on medium heat. [Tip:use a steel pan here so that you can notice the color change easily]
The butter will melt and start foaming/bubbling up. Keep stirring till the color of the butter changes to brown, it will take around 5-6 minutes.
Transfer the brown butter to a bowl and put it in the refrigerator to cool down a bit. You don't need to get it to solidify again, just cool down a little.
Using you hand mixer or stand mixer, beat together the butter and eggs for 3-4 minutes on medium speed.
Add granulated sugar and beat for another 2-3 minutes till well combined, scraping the sides of the bowl with a rubber spatula as and when required
Add the mashed bananas, sour cream, vanilla extract and mix till well combined.
Now add in the flour mix slowly and mix till just combined. Do not over-mix.
Fold in the chopped hazelnuts and chocolate chips and transfer batter to the prepared loaf pan.
Bake at 350 F degrees for 60-65 minutes or till a toothpick inserted in the center comes out clean. [After around 30 minutes, take out the bread from the oven and cover it loosely with aluminium foil to prevent excessive browning on the top and along the edges].
Transfer the bread on to a wire rack to cool completely.
Cut into slices once the bread and cooled down and enjoy with a cup of coffee!