In medium saucepan, slowly heat butter,
just until melted and golden, not browned,
stirring all the while.
Remove from heat.

Add flour, salt and pepper;
stir until smooth.
Add milk, a small amount at a time,
stirring after each addition.
Return to heat.

Over medium heat, bring to boiling,
stirring constantly. Reduce heat;
simmer 3 min.
Add mustard and grated cheese;
stir over low heat, just until cheese is melted
and sauce is hot.
Makes 3 cups.