Take a large thick-based saucepan and melt the butter over a very gentle heat.
Then add all the prepared vegetables, stirring them around to get them well coated. Cover with a tight-fitting lid, and with the heat kept very low let the vegetables sweat gently for about 15 minutes – if you give the pan a shake from time to time you won’t have any trouble with them sticking. After 15 minutes pour in the stock and add the Herbes de Provence and some seasoning. Then put the lid almost back on but leave a 1cm gap at the edge (to let some of the steam escape). Simmer the soup like this for about another 20 minutes, or until the vegetables are soft.
Now you can either sieve or liquidise half the contents of the saucepans, and then return them to the other half. This means that the soup will be thickened nicely and will still have some bits of vegetable in it for texture. Next, grill or fry the bacon rashers until crisp, and crumble them into the soup in little bits. I think this soup is nice served with some croutons crisp-fried in butter.