Step 1: Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan, or spray with a non-stick baking spray.
Step 2: In a large bowl, sift together the all-purpose flour, baking powder, baking soda, and salt. Whisk briefly to combine and set aside.
Step 3: In a separate large mixing bowl, using an electric mixer, cream together the softened unsalted butter and granulated sugar until light and fluffy, about 3-5 minutes. Scrape down the sides of the bowl as needed.
Step 4: Beat in the eggs one at a time, ensuring each egg is fully incorporated before adding the next. Beat in the vanilla extract.
Step 5: Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix on low speed until just combined. Be careful not to overmix, as this can lead to a tough cake.
Step 6: If desired, gently fold in any sprinkles or other 'dot' additions at this stage.
Step 7: Pour the batter evenly into the prepared baking pan and smooth the top with a spatula.
Step 8: Bake for 30-35 minutes, or until a wooden skewer or toothpick inserted into the center of the cake comes out clean.
Step 9: Remove the cake from the oven and let it cool in the pan on a wire rack for 10-15 minutes before inverting it onto the wire rack to cool completely.
Step 10: To make the frosting: In a medium bowl, beat the softened cream cheese and butter with an electric mixer until smooth and creamy, about 2-3 minutes.
Step 11: Gradually add the powdered sugar, one cup at a time, beating on low speed until combined, then increasing to medium speed until smooth.
Step 12: Beat in the vanilla extract. If the frosting is too thick, add milk or cream one teaspoon at a time until desired consistency is reached.
Step 13: Once the cake is completely cool, spread the cream cheese frosting evenly over the top.
Step 14: Garnish with extra sprinkles or decorative dots if desired. Slice and serve!