1. Place a rack in the center of the oven and preheat the oven to 350 degrees F. Generously grease two 9-inch round cake pans with solid vegetable shortening, then dust with flour. Shake out the excess flour. Set the pans aside.

2. Place the cake mix, sour cream, water, oil, eggs, and vanilla in a large mixing bowl. Blend with an electric mixer on low speed for 1 minute. Stop the machine and scrape down the sides of the bowl with a rubber spatula. Increase the mixer speed to medium and beat 2 minutes more, scraping down the sides again if needed. The batter should look well combined. Divide the batter between the prepared pans, smoothing it out with the rubber spatula. Place the pans in the oven side by side.

3. Bake the cakes until they spring back when lightly pressed with your finger, 28 to 32 minutes. Remove the pans from the oven and place them on wire racks to cool for 10 minutes. Run a knife around the edge of each layer and invert each onto a rack, then invert again onto another rack so that the cakes are right side up. Allow to cool completely, 30 minutes more.