Melt unsalted butter in a Dutch Oven over medium heat.
Add onions, carrots, and celery stirring as you add. Cook for about 5-6 minutes (until they start to soften) stirring occasionally.
Add in the garlic, rosemary, red pepper flakes, salt, and pepper stir. Continue to stir the ingredients when cooking for about 30 seconds.Sprinkle with flour over the vegetables while continuing to cook and stir. In about 1 minute the vegetables will turn to a medium blonde color.
Using the whisk slowly blend in 2 cups of the broth. (Continue to whisk until all lumps have been blended in.)
The soup will be thick.
Increase the heat while bringing the soup to a boil. Reduce to a simmer. Add in the potatoes and the bay leaf. Cook for about 20 minutes,partially covered. (The potatoes will be fork tender.) Reduce the temp to low. Remove the bay leaf.
Stir in the sour cream and cheese.
Taste test and add salt and pepper accordingly.
Garnish with chopped fresh parsley.