Combine butter and oil in a Dutch oven or other heavy soup pot over medium-high heat.
When the butter has melted, add the onion, reduce the heat to medium-low, and cook for 6-7 minutes or until the onion has softened but has not yet changed color.
Add the cabbage and cook 2-3 minutes or until the cabbage wilts.
Add the potatoes and stir to coat with the fat.
Add the chicken broth. Bring to a boil. Reduce heat to medium-low and simmer uncovered for 12-15 minutes or until the potatoes are fork-tender.
Turn the heat off for the next step.
Place flour in a heat-proof bowl. Add 1/2 cup of the cooking liquid and whisk to make a smooth slurry. Add small amounts of additional cooking liquid as necessary. Slowly whisk in the half-and-half.
Pour the flour slurry and half-and-half combination into the pot along with the caraway seed and stir. Return to a simmer and cook for 5-6 minutes or until thickened. (Soup will thicken more upon standing.)
Add the Dijon mustard, Worcestershire, hot sauce and salt and black pepper to taste. Sprinkle with chopped fresh parsley if desired.