01 - Preheat the 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 combined.
03 - In a large bowl, cream the butter and sugar together until light and fluffy, about 2-3 minutes.
04 - Beat in the eggs one at a time, then mix in the vanilla extract until fully incorporated.
05 - Stir in the sour cream until the mixture is smooth and uniform.
06 - Add the flour mixture in three additions, alternating with the milk, beginning and ending with the flour. Mix until just combined.
07 - Gently fold in the cranberries with a spatula until evenly distributed throughout the batter.
08 - Pour the batter into the prepared pan and smooth the top. Sprinkle with turbinado sugar and orange zest if using. Bake for 35-40 minutes, or until a toothpick inserted in the center comes out clean.
09 - Allow to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before serving.