01 - Preheat oven to 350°F. Grease a 9-inch round cake pan and line bottom with parchment paper.
02 - Combine cranberries, 1/3 cup sugar, water, and orange zest in small saucepan. Cook over medium heat, stirring occasionally, until cranberries burst and mixture thickens, 7-10 minutes. Cool slightly, then blend or mash to textured sauce.
03 - Whisk together gluten-free flour, almond flour, baking powder, baking soda, and salt in medium bowl.
04 - Beat butter and 3/4 cup sugar in large bowl until light and fluffy, 2-3 minutes. Add eggs one at time, beating well after each. Mix in vanilla extract.
05 - Add half flour mixture to wet ingredients, mixing just until combined. Mix in sour cream, then remaining flour mixture until smooth.
06 - Spread half batter evenly in prepared pan. Dollop half cranberry mixture over batter and swirl gently with knife. Repeat with remaining batter and cranberry mixture, swirling again.
07 - Bake 40-45 minutes until toothpick inserted in center comes out clean.
08 - Cool in pan 15 minutes, then remove and transfer to wire rack to cool completely. Dust with powdered sugar before serving if desired.