Create a rue by melting the butter in a sauce pan and adding the flour.  Add salt and pepper to taste and allow the flour to cook a bit.  When it is golden brown, whisk in the stock to create a white sauce.  Allow this to simmer while you boil water for the pasta.  When the pasta is almost to al dente and you are about ready to drain it, remove the white sauce from the heat and add the cheese to your white sauce and stir in a figure 8 to incorporate it all.  After draining your pasta, combine cheese sauce and noodles.  Serve warm!

Another variation of this would be to pour all of this into a baking dish once it's combined and sprinkle the top with buttered bread crumbs and bake for about 10-15 minutes (until the top is crusty).  Either way is delicious! ;)