Prepare pans: Preheat your oven to 350°F. Butter two 9-inch round cake pans thoroughly, dust with flour, and place a parchment paper round in the bottom of each. This prevents sticking. Set pans aside.

Mix dry ingredients: In a medium mixing bowl, whisk together 2 1/4 cups all-purpose flour, 2 1/2 teaspoons baking powder, 1/2 teaspoon baking soda, and 1/2 teaspoon salt. Set aside. Checkpoint: You should see an even, pale mixture with no lumps.

Cream butter and sugar: In a large mixing bowl, beat 3/4 cup softened unsalted butter and 1 1/2 cups granulated sugar together on medium speed for 3 minutes until the mixture looks pale, fluffy, and resembles frosting. Checkpoint: The mixture should have increased in volume by about half and look creamy, not grainy.

Add eggs: Add 3 room-temperature eggs one at a time to the butter mixture, beating well after each egg is added (about 30 seconds per egg). The mixture should be smooth and creamy after each addition. Checkpoint: All eggs should be fully incorporated with no streaks of egg white visible.

Alternate wet and dry ingredients: Working in batches, add one-third of the flour mixture to the butter mixture, beating on low speed for about 30 seconds until just combined. Then add half of the sour cream (1/2 cup), beat for 30 seconds. Repeat: another third of flour, remaining sour cream, final third of flour. Do not overmix. Checkpoint: The batter should be smooth and thick, with no visible streaks of flour.

Add citrus and vanilla: Pour in 1/2 cup fresh orange juice slowly while beating on low speed (about 30 seconds). Add 2 tablespoons orange zest and 1 teaspoon vanilla extract, mixing until just combined. The batter will be slightly thinner than before. Checkpoint: The batter should be smooth, slightly pourable, and smell strongly of orange.

Fill pans: Divide the batter evenly between the two prepared pans (about 2 cups per pan). Use an offset spatula to smooth the tops so they're level. This helps the cakes bake evenly.

Bake cakes: Place pans on the middle oven rack and bake for 25-30 minutes. The cakes are done when a toothpick inserted in the center comes out clean or with just a few crumbs, and the edges pull slightly away from the pan sides. The tops should spring back when lightly touched. Checkpoint: A toothpick inserted in the thickest part should not have wet batter on it.

Cool in pans: Remove pans from oven and let cool at room temperature for 15 minutes. You should see the cakes pull away from the pan edges.

Turn out cakes: Run a thin knife around the edges of each pan. Place a wire cooling rack on top of a pan and carefully flip it over so the cake falls onto the rack. Remove the pan and parchment paper. Repeat with the second cake. Let both layers cool completely at room temperature, about 1 hour. Checkpoint: Cakes should be cool to the touch before frosting.

Prepare heavy cream: Pour 2 cups heavy whipping cream into a large mixing bowl and beat on high speed for 2-3 minutes until stiff peaks form. The cream should look fluffy and hold its shape. Transfer to a separate bowl and refrigerate. Checkpoint: Peaks should stand up straight when you lift the beaters.

Beat cream cheese: In a large clean bowl, beat 8 ounces softened cream cheese (should be room temperature for smooth mixing) with 1/2 cup powdered sugar on medium speed for 1-2 minutes until smooth and fluffy. Do not overmix. Checkpoint: Mixture should be creamy with no lumps of cream cheese visible.

Add vanilla and orange liqueur: Add 1 teaspoon vanilla extract and 2 tablespoons orange liqueur (or additional orange juice) to the cream cheese mixture. Beat on low speed for 30 seconds until smooth. Checkpoint: The frosting should be thin enough to fold but still hold some structure.

Fold in whipped cream: Gently fold the whipped cream into the cream cheese mixture in two additions using a rubber spatula. Fold slowly and carefully to keep the frosting light and fluffy. Fold until just combined—do not overmix or the frosting will deflate. Checkpoint: The frosting should look light, fluffy, and pale orange-tinted, without streaks of white cream visible.

Assemble cake: Place one cooled cake layer on a flat serving plate or cake board. Using an offset spatula, spread a layer of frosting about 1/4 inch thick on top. Checkpoint: The frosting should cover the entire top layer evenly.

Stack second layer: Carefully place the second cake layer on top of the frosting. If the layers are slightly uneven, use frosting to level them.

Frost sides and top: Spread frosting over the top and sides of the cake in a smooth, even layer (this is called a crumb coat). You may use all remaining frosting. Work slowly and let the spatula do the work. Checkpoint: The entire cake should be covered with a thin, even layer of frosting.

Garnish: Top the cake with 1 tablespoon fresh orange zest and arrange fresh orange slices around the top for decoration. You can also add a light dusting of zest around the sides if desired.

Chill and serve: Refrigerate the finished cake for at least 30 minutes (or up to 4 hours) before serving. This firms up the frosting and makes slicing cleaner. Remove from the refrigerator 10 minutes before serving for the best texture and flavor.