Mix 1 cup cranberries with 2-3 tablespoons from 2 cups all-purpose flour. Reserve.
Sift the remaining flour, 2 teaspoons baking powder and ¼ teaspoon salt. Set aside. Or have the ingredients measured and sift them directly over the batter.
Beat 1 cup unsalted butteruntil creamy in a large bowl. Slowly add 1 ⅓ cups sugar and beat for 2 minutes.
Add 2 eggs one at a time, beating well after each addition. Scrape the sides of the bowl regularly for even mixing.
Add 1 tablespoon orange zest and ½ teaspoon vanilla extract.
Beginning and ending with dry ingredients, add them in 3 parts, alternating with 1 cup sour cream in 2 parts. So you start and end with the flour mixture.
Add the reserved cranberries with flour and stir them with a rubber spatula, integrating well until no flour spots remain. Don’t beat or crush the cranberries.
Pour the batter into the prepared pan and smooth the top.
Scatter the remaining ½ cup fresh cranberries over the batter. Sprinkle with 3 tablespoons light brown sugar.
Bake for about 45 minutes, or until a cake tester or toothpick inserted in the center comes out clean.
Let it cool on a wire rack for 15 minutes, and run a smooth-bladed knife carefully around the edges to loosen any stuck parts.
Let cool completely before glazing.