Peel and crush (mince) the garlic clove and peel and roughly chop the onion. Place all the ingredients (including a good dash of salt and a few twists of fresh pepper) into a pan and boil gently for about half-an-hour until the moisture reduces to about half of its original volume. Remove the bouquet garni then allow the liquid to cool. Place into a blender and 'liquidate' until it is completely smooth or, if you don't have a blender, press the mixture through a sieve (strainer) and reject the solid remnants.
Serve hot as a sauce for almost any pasta dish such as spaghetti, macaroni, fusilli, fettuccini, tortellini etc. It's also extremely good with Gnocchi or spätzle.