01 - Preheat oven to 350°F. Grease and line a 9x13-inch sheet pan with parchment paper.
02 - In a large bowl, whisk together all-purpose flour, granulated sugar, baking powder, baking soda, and fine salt.
03 - In a separate bowl, combine cream soda or root beer, melted unsalted butter, eggs, and vanilla extract. Whisk until well blended.
04 - Gently fold the wet ingredients into the dry mixture until just combined, being careful not to overmix.
05 - Pour batter into the prepared pan and smooth the surface. Bake for 28 to 32 minutes, or until a toothpick inserted in the center emerges clean.
06 - Allow the cake to cool completely in the pan on a wire rack before frosting.
07 - Using an electric mixer, beat softened butter until creamy. Gradually add sifted powdered sugar, then blend in cream soda or root beer, heavy cream, vanilla extract, and a pinch of salt until light and fluffy.
08 - Spread frosting evenly across the cooled cake.
09 - Decorate with maraschino cherries, rainbow sprinkles, and dollops of whipped cream if desired. Slice and serve.