In a Dutch oven, melt butter over medium heat. Add onion and cook for 4 minutes, or until soft.
Add cabbage, potatoes, broth, salt, pepper, and red pepper flakes.
Cover, reduce heat to medium-low and simmer for 10 minutes, stirring occasionally.
Remove lid and increase heat to medium-high. Cook until most of liquid has evaporated (about 12 to 14 minutes), stirring occasionally.
