Preheat oven to 350°F (180°C). Spray 2 (9-inch) round cake pans with baking spray with flour. Line bottom of pans with parchment paper.

In the bowl of a stand mixer fitted with the paddle attachment, beat butter, sugar, and orange zest at medium-low speed just until combined. Increase mixer speed to medium; beat until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add eggs, one at a time, beating well after each addition.

In a large bowl, whisk together flour, baking powder, salt, and baking soda. In a medium bowl, whisk together buttermilk, orange juice, and vanilla. With mixer on low speed, gradually add flour mixture to butter mixture alternately with buttermilk mixture, beginning and ending with flour mixture, beating until combined after each addition and stopping to scrape sides of bowl. Divide batter between prepared pans; using a small of set spatula, smooth tops. Forcefully tap pans on a kitchen towel-lined counter several times to settle batter and release as many air bubbles as possible.

Bake until a wooden pick inserted in center comes out clean, 30 to 38 minutes. Let cool in pans for 10 minutes. Remove from pans, and let cool completely, parchment side down, on wire racks.

Level cooled cake layers; discard parchment. Place 1 cake layer, cut side up, on a cake turntable or a serving plate. Brush with half of Simple Syrup. Spoon ½ cup (about 123 grams) Creamy Buttermilk Frosting into a pastry bag; cut a ½-inch opening in tip. Pipe a ½-inch-tall border around edge of layer; dollop and spread Orange Cream Filling inside piped border. Top with remaining cake layer, cut side down. Brush with remaining Simple Syrup. Spread a thin layer of frosting on top and sides of cake to create a crumb coat; refrigerate for 30 minutes.

Divide 2 cups (457 grams) Creamy Buttermilk Frosting between 2 small bowls. Add food coloring to 1 bowl, stirring until frosting is deep orange. Add food coloring to second bowl, stirring until frosting is light orange. Leave remaining frosting white.

Using a small of set spatula, spread deep orange frosting in an even layer over bottom third of sides of cake. Spread light orange frosting over middle third of sides of cake. Spread white frosting on top and top one-third of sides of cake. Holding a bench scraper or a large of set spatula flush against sides of cake, scrape off excess frosting until sides are smooth. Using a small of set spatula, swirl top as desired. Using a bench scraper or a large of set spatula held flush against sides of cake, scrape frosting one more time to give sides a smooth, finished look. Garnish with sprinkles, if desired.