1. Fill and boil your kettle. Trim the roots and any woody greens off the leeks, then halve them and rinse out any grit. Trim the dry ends off the celery, then thinly slice them. Trim and peel the carrots and parsnips, then thickly slice them on the diagonal.
2. Put a large pan or casserole dish on a medium heat. Add 2 tbsp olive oil and the chopped veg. Season with a good pinch of salt and pepper. Pop a lid on the pan. Gently cook, stirring often, for 10 mins till the veg have started to soften but haven't picked up too much colour. If they start to brown, turn the heat down and add a splash of water.
3. While the veg sweat, drain the mixed beans and rinse them under cold water. If you have heatproof kitchen string, you can tie the bouquet garni herbs together to make them easier to fish out when the stew is ready.
4. When the veg have fried for 10 mins, add the mixed beans and pearl barley to the pan. Stir to mix. Drop in the bouquet garni. Pour in 1½ ltr hot water from the kettle. Season again, stir to mix then pop the lid back on and bring to the boil. Turn the heat down and simmer the stew for 15 mins.
5. While the stew simmers, finely chop the parsley stalks and leaves. Tip the flour into a mixing bowl and add 1 tsp baking powder and a good pinch of salt and pepper. Whisk together with a fork.
6. Chop the butter and add it to the bowl, then rub it in with your fingertips till there are no lumps remaining. Add ¾ of the parsley to the bowl. Crumble the garlic & herb sheep's cheese into the bowl and add 4 tbsp cold water, then stir with a fork to bring the dough together. If the dough is a bit dry, add an extra 2-4 tbsp water.
7. Divide the dough into 8 pieces and shape into rounds. Carefully drop them into the stew. Pop the lid back on and simmer for 30 mins till the dumplings are cooked through and doubled in size and the barley is tender.
8. Taste the stew and add a pinch more salt and pepper, if you think it needs it. Ladle the stew and dumplings into warm bowls, discarding the bouquet garni, and garnish with the remaining chopped parsley to serve.