Preheat oven to 350°F. Generously coat 2 (8-inch) round cake pans with baking spray; line bottom of pans with parchment paper. Coat parchment with baking spray; set aside. Gather all ingredients.

Beat sugar and butter with an electric mixer on medium speed until light and fluffy, about 3 minutes.

Reduce mixer speed to low; add eggs, 1 at a time, beating until well blended after each addition, stopping to scrape down sides of bowl as needed. Add vanilla, and beat until combined, about 30 seconds.

Whisk together flour, cocoa, baking powder, baking soda, and salt in a medium bowl until no lumps remain. Add flour mixture to sugar mixture, in 3 additions, alternately with water, beginning and ending with flour mixture; beat on low speed after each addition until nearly combined, about 2 minutes total.

Fold in sauerkraut.

Divide batter evenly between prepared cake pans, and spread into an even layer.

Bake in preheated oven until a wooden pick inserted into center of Cakes comes out clean, about 30 minutes. Remove from oven; let cool completely in cake pans on a wire rack until room temperature, about 1 hour, 30 minutes.

Place chocolate in a large microwavable bowl; microwave on HIGH, stirring every 30 seconds, until fully melted, about 2 minutes total. Let cool slightly until chocolate is lukewarm, about 5 minutes, stirring occasionally.

Add cream cheese and heavy cream; beat with electric mixer on medium speed until fully combined, about 2 minutes. Gradually add powdered sugar, beating well after each addition. Add vanilla and salt; beat until combined.

To assemble, remove cooled Cakes from cake pans; discard parchment paper. Slightly trim tops of each Cake layer to create a flat surface. Place 1 Cake layer, cut side up, on a plate or cake stand; spread 1 ½ cups frosting in an even layer to edges of Cake using an offset spatula. Top with second Cake layer, cut side down.

Using a large offset spatula, spread remaining frosting evenly over top and sides of Cake, swooping and swirling in a decorative design.

Slice and serve.