Preheat your oven to 350°F (175°C) and grease a sheet pan (approx. 18x13 inches) with cooking spray or butter.

In a bowl, sift together the flour, baking powder, baking soda, and salt. Set aside.

In a large mixing bowl, use an electric mixer to cream the softened butter with both sugars (granulated and brown) until light and fluffy.

Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next. Mix in the vanilla extract.

Gradually add the dry ingredients to the butter and sugar mixture, alternating with buttermilk. Be and end with the dry ingredients. Mix until just combined.

Gently fold in the shredded coconut and chopped walnuts, making sure they are evenly distributed in the batter.

Spread the batter evenly in the prepared sheet pan. Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean. Allow to cool completely in the pan.

In a separate mixing bowl, beat the softened cream cheese and butter together until combined and creamy. Gradually add the powdered sugar, followed by the vanilla extract, mixing until smooth and fluffy.

Once the cake is fully cooled, spread the cream cheese frosting generously over the top. Optional: sprinkle extra coconut and walnuts on top for garnish.