Herby chicken stew with dumplings

Name: Herby chicken stew with dumplings
Prep time: 20 min
Cook time: 6 h
Total time: 6 h 20 min
Cuisine: European, British
Ingredients: Low calorie cooking spray; 500g chicken breast, diced; 1 onion, diced; 1 small leek, sliced; 600g potatoes; 3 carrots, sliced; 1tsp dried thyme; 3 chicken stock cubes; 150g self raising flour; 0.25 tsp baking powder; Sea salt; Black pepper; 3 egg yolks; 5-6 tbsp water; 0.5 lemon, juice; 1 tin butter beans; 50g fresh spinach