First, in a large cooking pot, melt the fat, then cook the bacon and onion in it for 5 minutes before adding the rest of the vegetables – give them a good stir round in the butter and let them colour a little at the edges over a fairly low heat. Then pour in the stock and add the washed split peas.
Bring everything back up to simmering point, skim the surface if there’s any scum, then put a lid on and continue to simmer very gently for about 11/2 hours, or until the peas are absolutely soft. Now liquidise the soup just a little (or else sieve it) – but it shouldn’t be too uniformly smooth. Taste, season, re-heat and serve the soup garnished with some croutons crisp fried in bacon fat. Note: There’s no need to soak the split peas, but the length of cooking time may vary 30 minutes or so either way.