Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan with butter or line it with parchment paper to ensure easy release of the loaf after baking.
In a medium mixing bowl, whisk together the flour, baking powder, baking soda, salt, and ground cinnamon until evenly combined. Set this mixture aside for later use.
In a large mixing bowl, use an electric mixer to cream the softened butter and granulated sugar together until the mixture becomes light and fluffy, about 2-3 minutes.
Add the eggs to the butter-sugar mixture one at a time, beating well after each addition to fully incorporate them. Stir in the vanilla extract until combined.
Gradually add the dry ingredient mixture to the wet ingredients, alternating with the buttermilk. Begin and end with the dry ingredients, mixing gently after each addition just until combined. Be careful not to overmix, as this will affect the texture.
Carefully fold in the fresh cranberries, chopped walnuts (if using), and grated orange zest until they are evenly distributed throughout the batter.
Pour the batter evenly into the prepared loaf pan, using a spatula to smooth the top for a nice finish.
Bake in the preheated oven for 55-60 minutes, or until a toothpick inserted into the center comes out clean. If the top of the loaf begins to brown too much, you can loosely cover it with aluminum foil for the last 10-15 minutes of baking.
Once baked, remove the loaf from the oven and let it cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.
Notes
For an extra touch, drizzle a simple glaze made from powdered sugar and a splash of fresh orange juice over the top.