Place A Rack In The Center Of The Oven, And Preheat The Oven To 350°F.
Lightly Grease And Flour Two 9″ Round Cake Pans.
Set The Pans Aside.
Drain The Liquid From The Sauerkraut.
Place It In A Colander Or Sieve And Rinse It Very Well Under Running Cold Water.
With Your Hands Or A Wooden Spoon, Push Excess Liquid Out Of The Sauerkraut And Let It Rest In The Sieve Or Colander Set Over The Sink.
Place The Butter And Sugar In A Large Mixing Bowl, And Blend With An Electric Mixer On Medium Speed Until Creamy, 2 Minutes.
Add The Eggs, One At A Time, Beating Well After Each Addition.
Scrape Down The Bowl With A Rubber Spatula And Fold In The Vanilla.
Sift Together The Flour, Cocoa, Soda, Cream Of Tartar, And Salt In A Medium-Size Bowl.
Add To The Creamed Mixture Alternately With The Water, Beginning And Ending With The Flour, Beating On Low Speed With The Mixer.
Remove The Sauerkraut From The Colander And Either Chop It With A Knife On A Cutting Board Or Pulse 20 Times In The Food Processor Fitted With A Steel Blade.
You Want To Break Up The Pieces But Not Puree Them.
Fold The Sauerkraut Into The Batter Until Just Combined.
Divide The Batter Between The Prepared Pans And Smooth The Tops With The Spatula.
Place The Pans In The Oven.
Bake The Cake Until It Just Pulls Away From The Edges And The Top Springs Back When Lightly Pressed In The Center, 25 To 30 Minutes.
Remove The Pans From The Oven And Place On Wire Racks To Cool For 10 Minutes.
Run A Sharp Knife Around The Edges Of The Pans, Give Them A Gentle Shake, And Invert Them Once And Then Again So They Cool Right Side Up On The Rack.
Cool For 30 Minutes Before Frosting.
To Assemble, Place 1 Layer On A Serving Plate And Spread About ⅔ Cup Of The Frosting Smoothly Over The Top.
Place The Second Layer On Top And Spread The Remaining Frosting On The Top And Sides Of The Cake.
Store In The Refrigerator For Up To 5 Days.
