In a saucepan, melt butter; remove from heat.
Blend in flour and salt, stirring until smooth.
Add both milks and heat, stirring constantly, until it thickens and becomes smooth.
Add Velveeta cheese and 1/2 of the shredded cheese. Heat until cheese is melted.
Combine cheese sauce with drained macaroni. Pour into a greased 2 quart casserole dish. Top with remaining cheese.
If desired, bake at 375° for 20-25 minutes until bubbly and rich brown.