Preheat the oven to 350 degrees F. Line 9x5-inch loaf pan with parchment paper leaving an overhang on the two longer sides, set aside.

In a large bowl, whisk the 1 ¾ cup flour, cocoa powder, sugar, baking powder, baking soda, and kosher salt together. Set aside.

In a separate medium-sized bowl, whisk together the mashed bananas, eggs, vanilla extract, vegetable oil, and sour cream until well combined.

In a small bowl, toss the 2 tablespoon flour together with the walnuts until the walnuts are well coated with flour.

Add the wet ingredients to the dry ingredients with a silicone spatula until just combined, a little dry flour is okay to see as it'll be mixed in with the walnuts. Gently fold in the walnuts then pour the batter into your prepared loaf pan.

Bake the chocolate banana bread for 45-55 minutes, until a toothpick inserted comes out clean. Remove the bread from the oven and allow it to cool in the pan for 10 minutes before using the parchment paper overhangs to lift the loaf out of the pan and onto a wire rack to cool completely.

Slice and serve warm or room temperature.

Keep tightly wrapped in plastic wrap at room temperature to keep fresh for five days.