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 - Add eggs one at a time, mixing well after each addition. Stir in vanilla extract until fully blended.
05 - Mix sour cream into butter mixture until smooth and uniform in texture.
06 - Add flour mixture in three portions, alternating with milk, starting and ending with flour. Mix until just combined.
07 - Gently fold cranberries into batter using spatula, being careful not to overmix.
08 - Transfer batter to prepared pan, smoothing top surface. Sprinkle with turbinado sugar and orange zest if desired. Bake for 35-40 minutes until toothpick inserted in center comes out clean.
09 - Let cake rest in pan for 10 minutes, then remove to wire rack to cool fully before serving.