Preheat the oven to 350 and prepare a loaf pan with grease and parchment paper. Set to the side.
Melt the butter in the microwave or on the stove over medium-heat. Remove from the heat and allow the butter to cool to room temperature.
Zest the two oranges using an orange zester. Place the zest in a bowl and set to the side.
In a large bowl, mix the brown sugar, granulated sugar, and eggs with a whisk. Add in the sour cream and vanilla and mix until smooth.
Add in the flour, baking powder, baking soda, and salt. Mix with a whisk until fully combined.
Use a rubber spatula to fold in the cranberries, walnuts, and orange zest. Mix until fully distributed.
Pour the batter into the prepared pan and bake the cake in the oven for 55-65 minutes. A toothpick will run clean when the cake is fully baked.
Allow the cake to cool fully in the pan on a cooling rack before removing it from the pan. Then, slice and enjoy!