What you need:
One stick of butter
amounts of high quality parmesan cheese
. (Note: if you get cheap cheese or pregrated cheese it will not work nearly as well)
One pint of whipping cream (not whipped, obviously).
Salt and pepper.
What you do:
Melt one stick of butter in a reasonably deep pan. Make absolutely sure you don't burn it. THIS IS KEY.
Cut two cloves of garlic in half and put them in the butter. Let them cook for a little while making sure the butter doesn't burn.
Pour the cream into the pan and stir until the butter and cream are no longer separated. Wait until the cream is nice and hot before going on to the next step (It should start to produce steam).
Slowly pour in roughly 2-3 cups of finely grated cheese while stirring. Pour in a little, stir til it melts, then pour some more in, etc etc etc.
Now just let it simmer (keep stirring it) until it gets to the thickness you desire. Season with salt and pepper to taste. Keep in mind that it's not gonna be great the first time you do it, it takes a little practice.