Cook the pearl barley in boiling, salted water for about 50 minutes, or until tender but still with a little bite, then drain and leave to steam dry.
Next, heat a glug of olive oil in a frying pan and add the onion and a pinch of salt. Cook slowly on a low heat for about 10 minutes, without coloring too much. Add the barley and the peas. Cover with the stock and bring to the boil. Simmer for 10 minutes, stirring every now and then.
On a board, mash the flour and butter together with a fork until you have a paste. This is called a "beurre manie" and it's a great way of thickening stews or sauces without having to stir the flour in directly, which could give you lumps. Stir half of the paste into the peas and barley and continue to simmer until the liquid begins to thicken. If, after 5 minutes, it's not thick enough, add some more of your beurre manie. What you want to achieve is a silky smooth broth. Continue to simmer for another 10 minutes, adding a little extra stock if it gets too dry, while you cook your partridges.
Put some olive oil into another frying pan. Season the partridge legs with salt and pepper and add them to the pan. (The legs go in first because they're tougher than the breasts and need longer to cook.) Shake them about and, after a few minutes, when they're lightly golden, add the bacon bits and stir gently to stop them catching on the bottom. Meanwhile, lay the partridge breasts out, sprinkle over the chopped thyme and press onto both sides with a good pinch of seasoning. When the bacon is lightly golden, push it to 1 side of the pan with the partridge legs and lay the breasts in, skin side down. Cook for 4 minutes, then turn and cook on the other side for a minute to give you crispy skin and moist meat. You can cook them for longer if you like your meat well done.
When the breasts are done, taste the barley broth and adjust the seasoning, then stir in the lettuce and arugula - they only need a minute or so to cook. Serve the barley, peas and lettuce with the partridge breasts and legs on top and sprinkle with the bacon pieces. Spoon the broth juices over the top. Lovely homey cooking!
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