2 tbsp. Butter
Sprinkle in flour and whisk together until combined. Cook over low heat for 2 minutes.
Pour in milk and beer, whisking constantly, and cook for an additional minute. Add mustard, paprika, and cayenne and whisk.
Add cheese and whisk slowly, cooking for a couple of minutes or until smooth, melted, and very hot.
Serve immediately (while hot) over toast. Sprinkle with chopped chives before serving.