Lightly grease a standard-size loaf pan and line it with a parchment paper sling.
In a medium-sized mixing bowl, beat together the 4 tablespoons unsalted butter, ¼ cup vegetable oil, and ⅔ cup granulated sugar until smooth. Add the 2 large eggs one at a time, beating to combine.
Stir in the 1 ½ teaspoons baking powder, ½ teaspoon baking soda, ½ teaspoon cinnamon, ¾ teaspoon fine sea salt, and ¾ cup sour cream.
Cut the cranberries in half. Measure out ¼ cup of the 2 cups gluten free flour and toss it with the 1 cup cranberries, then stir in the remaining flour to the batter. Now gently fold in the floured cranberries and the ½ cup walnuts.
Pour the batter into the prepared pan, using a rubber spatula to smooth the top. Preheat the oven to 350℉ and rest the batter while the oven heats. Then, place the loaf in the oven and bake for 55-65 minutes, until set and a tester inserted in the middle of the loaf comes out clean.
Cool the bread in the pan on a wire rack for 20 minutes, then turn it out onto the rack to cool completely.
Notes
Skip the nuts. Yes, this wouldn't be a cranberry walnut bread without the walnuts, but it's totally OK to leave out the nuts and make it into a simple cranberry bread.
Make mini loaves. This recipe bakes beautifully into 2 small loaves. I like to bake a double batch and give them away as edible holiday gifts.
Rest the batter. Hydrate that gluten-free flour by letting the batter rest while the oven heats, or even better, for up to 20 minutes. This will produce a smoother, more tender crumb without any grittiness.
Use dried cranberries. You can absolutely substitute 1 cup of dried cranberries for the fresh berries. I like to roughly chop the dried berries if I do this. Or, you could try a mix of fresh and dried berries.
Another berry. Use this recipe as your base for other fruit such as blueberries, raspberries, or blackberries in season.