Heat the butter in a frying pan, add the spring onions and fry for 5 minutes or until softened.
Reduce the heat to low and stir in the cheese, beer and mustard. Season well with pepper, then stir slowly for 3–4 minutes or until the cheese has melted.
Meanwhile, toast the bread lightly on both sides and place on a grill pan. Pour the cheese mixture over the toast and cook under a preheated hot grill for 1 minute or until bubbling and golden. Serve with a salad of Little Gem lettuce, radishes and tomatoes.