1. Soup Heat a heavy-based saucepan over medium heat. Add the butter and allow to melt before adding the onions. Reduce the heat and slowly cook the onions until golden brown and caramelised. Add the thyme and stir through the onions. Add the cider and continue to cook until it reduces to syrup. Add the chicken stock and continue to cook over low heat for 40 minutes, skimming the surface frequently. Season with salt and pepper.
2. Toasties Preheat the grill. Toast the bread under the grill on both sides. Sprinkle the grated cheese over four slices of ciabatta and place under the grill until melted. Place the remaining four slices on top of the melted cheese and cut in half.
3. Remove the thyme stalks from the soup and discard. Divide the soup between four warm bowls. Serve the cheese toasties on the side.