Start by browning sausage in a pan over medium heat. While they are browning, set stock to lightly boil in a large pot. Once both sides of the sausage are brown, remove from pan and let cool. Turn heat up to high and sear mushrooms to give them a little color. After about 3 minutes turn heat down to medium and add onions. Remove them before the mushrooms release their liquid (about 5 minutes total). Add mushrooms and onions to the stock. Cut sausage into half-inch pieces and add to the stock. Add a couple sprinkles of crushed red pepper (optional) and let simmer for 10 minutes. Add the cauliflower and broccoli and simmer for another 3-5 minutes.