In a large pot, cook macaroni according to manufacturers directions.
While macaroni is cooking, melt butter in a medium sauce pan over medium heat.
Add diced onion and cook till translucent/clear, being careful not to brown onion.
When onion is translucent/clear, remove from heat and add cracker crumbs and stir.
Reduce heat to low, return pan to stove, add milk and stir.
To cracker an milk mixture, add cheese that has been cut into small cubes (or you can shred it, allowing for faster melting).
Stir constantly (so that it does not burn) until cheese is thoroughly melted and incorporated in to a smooth mixture.
Remove macaroni from heat and drain. Do not rinse.
Carefully combine cheese mixture and macaroni together.
Serve as is or, if you are like me and like a crunchy top, transfer the mixture to a buttered baking dish, top with more buttered, crushed, cracker crumbs and bake uncovered in a pre-heated 350 degree oven for 1/2 hour.
Be prepared, you will never make macaroni and cheese any other way again!!!!