01 - Preheat oven to 350°F. Grease and line a 9x5-inch loaf pan with parchment paper.
02 - Combine cranberries, sugar, water, and orange zest in a small saucepan. Simmer over medium heat for 6 to 8 minutes, stirring frequently, until cranberries burst and mixture thickens. Remove from heat and cool.
03 - In a medium bowl, whisk together gluten-free flour, baking powder, baking soda, and salt.
04 - Beat butter and sugar in a large bowl until light and fluffy. Add eggs one at a time, mixing thoroughly after each addition. Stir in sour cream and vanilla extract.
05 - Add dry ingredients to the wet ingredients, mixing just until incorporated. Avoid overmixing to maintain a tender crumb.
06 - Spoon half of the batter evenly into the prepared pan. Drop half the cranberry mixture over the batter in dollops and swirl gently with a knife. Repeat layering and swirling with remaining batter and cranberry mixture.
07 - Bake for 35 to 40 minutes or until a toothpick inserted in the center comes out clean. Let cool in the pan for 10 minutes before transferring to a wire rack to cool completely.
08 - Whisk powdered sugar with orange juice until smooth. Drizzle over cooled cake before slicing.