Melt butter in a large sauce pan. Add diced onion and cook until soft, about 10 minutes. Pour in tomatoes (open can first). Add chopped red bell peppers, and red pepper flakes.
Next, the stock needs to make its way to the pot. Pour it in, stir, return to boil. Reduce heat to a fast simmer. Stir occasionally Part of the liquid will evaporate and condense the flavors.
Simmer for 30 minutes.
Puree with an immersion blender. Or regular blender. Or food processor. Use whatever you have. I prefer an immersion blender because it appeals to my lazy side. Firstly, you just stand right up there and puree the stuff in the same pot from whence it got cooked. Secondly, no transferring from pot to blender or food processor. I always burn the stew out of myself trying to do that.
Taste for seasoning and adjust.
Ladle into soup bowls. Garnish with crab meat. Serve. Enjoy the applause.