Boil macaroni according to box. Drain, dump in a bowl and set aside.
Using the same pan or a separate pan, melt butter and whisk in flour. Watch so it doesn't burn around 3 minutes. Slowly add milk and whisk till no lumps.
Add in chunks of Velveeta cheese stirring constantly till melts. Do not leave alone or will burn. Mix in dry mustard and pepper.
Add cooked macaroni to cheese mixture and stir together. Add more milk and cheese if needed.
Serve warm and enjoy!
Notes
To Store: Place leftovers in an airtight container. Store in fridge and consume within 3 days. Reheat to desired temperature over low heat or microwave. Add some milk if dry.
To Freeze: Place in freezer safe container and freeze up to 2 months. Thaw in fridge overnight. Add some milk if dry.