Summarize this article in one sentence.
Skim and discard any meat scum that is floating on the surface of the stock. Meanwhile, strain the stock through a fine sieve and throw out the bones and vegetables. Set the stock aside. After the brisket is cooled, chop it into bite sized pieces. Set aside.    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/1\/1c\/Make-Shchi-Step-3Bullet1.jpg\/v4-460px-Make-Shchi-Step-3Bullet1.jpg","bigUrl":"\/images\/thumb\/1\/1c\/Make-Shchi-Step-3Bullet1.jpg\/aid1127804-v4-728px-Make-Shchi-Step-3Bullet1.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/en.wikipedia.org\/wiki\/Fair_use\">Fair Use<\/a> (screenshot)<br>\n<\/p><\/div>"} and place over medium-high heat. Heat the oil.  Add the onions and sauté for 3-4 minutes or until wilted.    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/a\/a2\/Make-Shchi-Step-4Bullet1.jpg\/v4-460px-Make-Shchi-Step-4Bullet1.jpg","bigUrl":"\/images\/thumb\/a\/a2\/Make-Shchi-Step-4Bullet1.jpg\/aid1127804-v4-728px-Make-Shchi-Step-4Bullet1.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/en.wikipedia.org\/wiki\/Fair_use\">Fair Use<\/a> (screenshot)<br>\n<\/p><\/div>"}  Add the cabbage and sauté for an additional 4-5 minutes until it's cooked down and wilted.    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/7\/78\/Make-Shchi-Step-4Bullet2.jpg\/v4-460px-Make-Shchi-Step-4Bullet2.jpg","bigUrl":"\/images\/thumb\/7\/78\/Make-Shchi-Step-4Bullet2.jpg\/aid1127804-v4-728px-Make-Shchi-Step-4Bullet2.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/en.wikipedia.org\/wiki\/Fair_use\">Fair Use<\/a> (screenshot)<br>\n<\/p><\/div>"} Bring to a boil. After boiling, reduce the heat to medium-low, cover and simmer for 20 minutes.    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/f\/f8\/Make-Shchi-Step-5Bullet1.jpg\/v4-460px-Make-Shchi-Step-5Bullet1.jpg","bigUrl":"\/images\/thumb\/f\/f8\/Make-Shchi-Step-5Bullet1.jpg\/aid1127804-v4-728px-Make-Shchi-Step-5Bullet1.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/en.wikipedia.org\/wiki\/Fair_use\">Fair Use<\/a> (screenshot)<br>\n<\/p><\/div>"}  Enjoy!

Summary:
In a large heavy bottomed pot, combine all the stock ingredients and bring to a boil over medium high heat. Once the stock is boiling, reduce the heat to medium-low and simmer for 3 to 4 hours. Remove the beef brisket from the pot and set it aside in a bowl to cool. Clean the pot Pour in the stock slowly and add the chopped brisket. Add in the potatoes, tomatoes, salt and pepper and simmer for an additional 20 minutes. Serve hot among bowls with a slice of hearty rye bread and garnish with a dollop of sour cream.