01 - Preheat the oven to 350°F. Grease a 9-inch round or square cake pan with butter and line the bottom with parchment paper for easy removal.
02 - In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until thoroughly combined. Set aside.
03 - In a large bowl, beat the softened butter and granulated sugar together using an electric mixer or whisk until the mixture becomes light and fluffy, approximately 2-3 minutes.
04 - Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract until fully incorporated.
05 - Stir in the sour cream and mix until the batter is smooth and uniform in texture.
06 - Gradually add the flour mixture in three portions, alternating with the milk. Begin and end with the flour addition. Mix gently until just combined, being careful not to overmix.
07 - Gently fold the cranberries into the batter using a spatula, taking care to distribute them evenly throughout the mixture.
08 - Pour the batter into the prepared pan and smooth the top surface. If desired, sprinkle with turbinado sugar and orange zest. Bake for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
09 - Allow the cake to cool in the pan for 10 minutes. Carefully transfer to a wire rack to cool completely before slicing and serving.