Preheat the slow cooker if necessary; see the manufacturer's instructions. Put the pearl barley, onion, garlic and butternut squash into the slow cooker pot. Add the stock and a little salt and pepper. Cover with the lid and cook on low for 6–8 hours or until the barley and squash are tender.
Meanwhile, make the blue cheese butter. Put the butter on a plate, crumble the cheese on top, add the garlic and chillies and mash together with a fork. Spoon the butter into a line on a piece of nonstick baking paper, then wrap it in paper and roll it backwards and forwards to make a neat sausage shape. Chill in the refrigerator until required.
When almost ready to serve, stir the risotto, slice half the blue cheese butter and add to the slow cooker pot. Mix together until just beginning to melt, then add the spinach. Replace the lid and cook, still on low, for 15 minutes or until the spinach has just wilted. Ladle into shallow bowls and top with slices of the remaining butter.