In a medium bowl, whisk together all-purpose flour, baking powder, and salt until evenly combined.
Wet Ingredients
In a large bowl, cream softened butter and granulated sugar together until light and fluffy, about 3 to 4 minutes.
Add eggs one at a time, beating well after each addition. Stir in vanilla extract and orange zest.
Alternate adding the dry ingredients with sour cream to the butter mixture, beginning and ending with the dry ingredients. Mix until just combined.
Mix-ins
Gently fold fresh cranberries and chopped walnuts into the batter until evenly distributed.
Pour the batter into a greased and floured 9×5-inch loaf pan and smooth the top.
Bake in a preheated 350°F (175°C) oven for 60 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to rest in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.
Notes
Chilling the prepared batter for 30 minutes before baking helps keep the cranberries suspended in the loaf.Store sliced cake in an airtight container at room temperature for up to 3 days, or freeze individual slices for up to 2 months.