01 - Preheat oven to 350°F. Grease a 9-inch round or square cake pan and line the bottom with parchment paper.
02 - In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until well blended.
03 - In a large bowl, beat the softened butter and granulated sugar together until light and fluffy, approximately 2-3 minutes.
04 - Beat in the eggs one at a time, fully incorporating each before adding the next. Mix in the vanilla extract.
05 - Stir in the sour cream until the mixture is smooth and uniform.
06 - Add the flour mixture in three portions, alternating with the milk, beginning and ending with the flour. Mix until just combined, being careful not to overmix.
07 - Gently fold the cranberries into the batter using a spatula, distributing them evenly throughout.
08 - Pour the batter into the prepared pan and smooth the top surface. Sprinkle with turbinado sugar and orange zest if desired.
09 - Bake for 35-40 minutes, or until a toothpick inserted into the center emerges clean.
10 - Allow the cake to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before serving.