In a large pot, melt the remaining 4tbsp butter over medium heat. Add flour and whisk for 3 to 4 minutes or until flour begins to thicken. Slowly pour in stock, whisking the entire time. Repeat with milk. Bring mixture to a simmer for 20 minutes, or until mixture is thick and reduced slightly.
Add broccoli, carrots, potatoes, salt, pepper, paprika and mustard. Let simmer for 20 to 25 minutes, or till vegetables are tender. Take off heat and add cheese. Stir till melted. Serve immediately with extra cheese for garnish. Store in fridge in airtight container for up to a week. Reheat gently in microwave or over stovetop.
Recipe by pretty plain janes at https://prettyplainjanes.com/2016/02/18/broccoli-cheese-potato-soup/