Melt the butter in a small frying pan over low heat. Add the flour and cook for 1–2 minutes or until sandy in texture. Gradually whisk in the milk, add the cheese and cook, stirring, for 3–4 minutes or until thickened. Set aside.
Spread half the bread slices with the mustard and top with the extra cheese and ham. Spread the remaining slices with the cheese mixture and sandwich. Spread the sandwiches with butter on both sides. Heat a large non-stick frying pan over high heat and cook the sandwiches for 2–3 minutes each side or until golden and the cheese is melted. Makes 4.