Preheat your oven to 325F. Grease and flour your 9x5 inch loaf pan. Alternatively, you can line the pan with parchment paper. Add the butter, sour cream, cream cheese, and vanilla extract to the bowl of a stand mixer and beat on medium-high using the paddle attachment until well-combined, smooth, and creamy. Scrape the bottom and sides of the bowl and then add in the eggs. Beat well on medium-high speed until fully combined. Mix together the dry ingredients into a separate bowl.