Preheat the oven to 350°F / 176°C. Lightly grease the loaf pan (9"x 5") with softened butter & flour or line the inside of the pan with parchment paper.
Place chopped walnuts in the food processor. Press pulse for 5 seconds or until the nuts are into tiny/crumble pieces.
1 cup walnuts
In a bowl combine flour, salt, baking soda, cinnamon & baking powder together. Set aside until ready to use. (I highly recommend weighing your flour and sifting the dry ingredients before adding to the wet ingredients, this will make the batter fluffy and not lumpy).
1 ½ cup all-purpose flour (218g), 2 tsp baking powder, 2 tsp ground cinnamon, ½ tsp baking soda, ½ tsp salt
In a bowl: add butter, white sugar, brown sugar and mix well. Add eggs, vanilla extract, sour cream, and mix everything together. Add dry ingredients and walnuts. Mix everything together until well combine.
1 cup sour cream (full fat), ¾ cup brown sugar, ½ cup unsalted butter, ¼ cup granulated sugar, 1 ½ tsp vanilla extract, 2 large eggs
Transfer the batter to the pan. Bake for 50-55 minutes or until a toothpick placed in the center of the bread comes out clean (tent with aluminum foil after 35 minutes, if it's getting too brown on top). Remove from the oven and rest the bread in the pan for 15 minutes before transferring the loaf to a cake rack to finish cooling.