01 - Preheat oven to 350°F. Grease a 9-inch round or square cake pan and line bottom with parchment paper.
02 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl until evenly distributed.
03 - Beat softened butter and granulated sugar in a large bowl until light and fluffy, approximately 2–3 minutes.
04 - Incorporate eggs one at a time, mixing thoroughly after each addition. Blend in vanilla extract.
05 - Stir sour cream into batter until completely smooth and uniform.
06 - Add flour mixture in three portions, alternating with milk, starting and ending with flour mixture. Mix until just incorporated.
07 - Gently fold cranberries into batter using spatula, taking care not to overmix.
08 - Pour batter into prepared pan, level surface, and sprinkle with turbinado sugar and orange zest if using.
09 - Bake for 35–40 minutes or until toothpick inserted into center emerges clean.
10 - Let cake rest in pan for 10 minutes before transferring to wire rack to cool completely.