Preheat your oven to 350°F (175°C). Grease the 9-inch round cake pan and line the bottom with parchment paper for easy removal.
In a mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.
Add the eggs one at a time to the butter-sugar mixture, beating well after each addition. Then, mix in the vanilla extract.
In another bowl, whisk together the flour, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the wet mixture alternately with the buttermilk, starting and ending with the flour mixture. Mix until just combined, being careful not to over-mix.
Gently fold in the fresh cranberries using a rubber spatula.
Pour the batter into the prepared cake pan, smoothing the top with the spatula.
Bake in the preheated oven for 40-45 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, remove the cake from the oven and allow it to cool in the pan for 10 minutes. Then, turn it out onto a wire rack to cool completely.
If desired, dust the cooled cake with powdered sugar before serving.