Place a small saucepan of water over high heat and bring to a boil. Add the dried barley to the saucepan, reduce the temperature to low and simmer for 35 minutes. Once cooked, drain the barley and set aside.
Heat 2 teaspoons of extra virgin olive oil in a large pot over high heat. Add the chicken breast and cook until lightly browned. Remove the chicken from the pot and set aside for later.
Heat the remaining 2 teaspoons of extra virgin olive oil in the large pot. Add the garlic, and cook for 1 minute or until it becomes lightly golden and fragrant.
Add the leek, carrot, mushroom, and and fresh thyme to the pot. Cook while stirring occasionally for 5 minutes or until the mushroom and leek has wilted.
Pour the white wine into the large pot and cook, stirring occasionally until the liquid almost completely evaporates.
In a small bowl/jug, add the chicken stock, milk, Dijon and wholegrain mustards, and cornflour. Stir to mix the sauce ingredients. Pour the sauce mix into the large pot and stir it through the vegetables. Once the liquid starts to thicken and bubble, place the lid on the pot, reduce the heat to medium and simmer for 15-20 minutes or until the carrots have softened.
Return the chicken to the pan and simmer for a further 2 minutes.
Add the cannellini beans and cooked barley to the pot. Mix and remove from the heat.
Serve topped with cracked black pepper and crusty bread. Enjoy!