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 well blended.
03 - Beat softened butter and granulated sugar in a large bowl until light and fluffy, approximately 2 to 3 minutes.
04 - Add eggs one at a time, beating thoroughly after each addition. Mix in vanilla extract until fully combined.
05 - Stir sour cream into the butter mixture until smooth and uniform in texture.
06 - Add flour mixture in three portions, alternating with milk in two additions. Begin and end with flour mixture, mixing only until just combined.
07 - Gently fold cranberries into batter using a spatula, being careful not to overmix.
08 - Pour batter into prepared pan, smoothing surface with spatula. Sprinkle turbinado sugar and orange zest evenly over top if desired.
09 - Bake for 35 to 40 minutes until a toothpick inserted in center emerges clean.
10 - Let cake rest in pan for 10 minutes, then transfer to wire rack to cool entirely before slicing and serving.