In a large pot, fry the bacon pieces over medium-high heat until crisp. Drain the bacon on a paper towel and set aside. Pour off the grease and return the pot to the stove.
Add the onions to the pot and cook over medium-high heat for 3 to 4 minutes. Add the cauliflower, sprinkle with the Cajun spice and 1/2 teaspoon black pepper and cook, stirring, until the cauliflower starts turning golden brown, another 3 to 4 minutes. Stir in the chicken broth, bring to a boil, reduce the heat to a simmer and cook for 15 minutes.
Use an immersion blender to puree the mixture slightly, or all the way if you prefer. (Or use a regular blender; just don't fill too full.)
In a separate saucepan or skillet, melt the butter. Sprinkle in the flour and whisk to form a paste. Pour in the milk, then continue cooking until it thickens. Remove from the heat and stir in the half-and-half.
Pour the white sauce into the soup. Turn the heat to medium high and bring back to a boil for 3 to 5 minutes. Reduce the heat to low, stirring in the cheese and sour cream until the cheese is fully melted. Stir in the parsley.
Taste and adjust the seasoning. Serve with a little extra cheese, a sprinkle of bacon and a sprinkle of parsley.