If you are using hulled barley, soak it overnight (or for at least 8 hours), rinse well and drain. Skip this step if you are using pearl barley.
In a medium pot, sauté the onions and carrots in 1 tablespoon of butter until softened and fragrant. Season well with salt and pepper.
While the onions and carrots are cooking, melt the rest of the butter in a large frying pan and fry the sliced hearts until cooked. Season well and set aside.
Once the onions and carrots are softened, add the crushed garlic cloves and bay leaf to the pot. Stir around for a couple of minutes.
Stir in the barley, chicken hearts and a little more salt.
Pour in 5 cups of the stock. Your soup will look thin - don't worry, it will thicken a lot as the barley cooks.
Bring the soup to boil, then reduce to simmer and cook for about 30 minutes until the carrots and the barley are soft. Check on it halfway through cooking, if it is getting too thick, pour in the last cup of stock.
Once the veggies are tender, adjust the seasoning and serve the soup hot, garnished with some fresh chopped herbs if you like.