Preheat and Prepare the Pans: Preheat your oven to 350°F (175°C). Lightly spray two 8- or 9-inch round cake pans (or one 9×13-inch pan) with nonstick baking spray. This helps the cakes release cleanly and keeps them soft and moist.
Mix the Batter: In a large mixing bowl, combine the yellow cake mix, reserved mandarin orange juice (use the liquid from the can and add water if needed to make a full cup), oil, and eggs. Beat with an electric mixer on medium speed for about 2–3 minutes, or until the batter is smooth and slightly thickened. The oranges will add moisture and a subtle citrus aroma that lightens the cake beautifully.
Fold in the Oranges: Gently fold in the drained mandarin orange segments. Their delicate texture adds little bursts of flavor throughout the cake without overpowering it.
Pour and Bake: Divide the batter evenly between the prepared pans. Smooth the tops with a spatula for even baking. Bake for 25 minutes, or until a toothpick inserted in the center comes out clean and the cakes are lightly golden. If using a 9×13-inch pan, baking time may be closer to 30 minutes. Be careful not to overbake — this cake should stay moist and tender.
Cool Completely: Let the cakes rest in the pans for about 10 minutes before transferring them to a wire rack to cool fully. The frosting is whipped and light, so applying it before the cakes are cool can cause it to melt.
