Microwave mac 'n' cheese

So today's meal was some bbq ribs in the slow cooker Thanks to my taste of home magazine.  It had this mac 'n cheese recipe listed for "on the side."  I have yet to try a microwave mac 'n cheese so how could I resist trying this one.  It was Awesome!  Glad we tried it.  I am posting it first because I did make some changes and I don't want to forget what I did.  I loved that this cooked while the ribs heated in their bbq sauce.  Worked out perfect.

Ingredients

• 2 cups elbow macaroni (I used a Barilla - I love their pasta and their elbows have a cute little twist.)
• 2 cups hot water
• 1/4 cup butter
• 1 Tablespoon dehydrated onions
• 1/2 teaspoon salt
• 1/4 teaspoon ground mustard
• 1/4 teaspoon pepper
• 1 1/4 cup milk (I used fat free)
• 1/3 cup flour
• 6 oz. 2 % velveeta
• 2 oz. sharp cheddar

Directions

1. In a medium large microwave safe dish (I used a pyrex bowl) combine macaroni, water, butter, onion, salt, pepper and mustard.  (I just stuck the cube of butter in the middle without doing anything to it - seemed to work fine.)  Cover and microwave on high for 3 minutes (I only covered it with the little cover I use to cover a plate when reheating - it fit right on top of my bowl - not tightly or anything, but again, seemed to work fine.)
2. Stir.  Cover and cook at 50% power for 3 minutes.  
3. Meanwhile, combine flour and milk.  Gradually stir milk mixture into macaroni mixture.  Add cheeses.  
4. Cover and cook 3 minutes, stir, cover and cook 3 minutes.