Place potatoes in a medium sized pot with 2 litres (4 litres for 4 servings) salted water. Bring to a boil and cook for 15-18 minutes, or until fork tender.
Drain chicken thighs and pat dry with paper towel. Season well with salt and pepper.
Wash green beans, Italian parsley, and lemon. Trim ends off of green beans. Pick and chop parsley leaves. Zest half of the lemon and cut in half. Dissolve chicken stock cube in ¼ cup (½ cup for 4 servings) water.
Heat 2 tbsp. (4 tbsp. for 4 servings) oil in a large skillet over medium-high. Cook chicken thighs for 3-4 minutes each side or until golden. Remove chicken from skillet. Add onion and cook for 1 minute, scraping bottom of skillet with a wooden spoon. Add herb blend, grainy mustard, half of the garlic, and stir until fragrant. Add flour and cook while stirring for 1 minute. Stir in stock mixture and bring to a simmer. Reduce heat and stir in ½ cup (1 cup for 4 servings) milk and parmesan. Add lemon zest and half of the lemon juice to taste. Season to taste with salt and pepper. Put chicken thighs in gravy and cook for 5 minutes, or until chicken has internal temperature of 165°F.
Cook Green Beans
When potatoes from Step 1 are almost fork tender, add green beans to same pot. Cook for 2 minutes or until tender and bright green. Drain vegetables through a fine mesh sieve and place back into pot. Season with remaining garlic, 2 tbsp. (4 tbsp. for 4 servings) butter, and salt and pepper to taste.
Divide green beans and potatoes onto plates with chicken thighs. Spoon gravy on top of chicken and garnish with parsley. Enjoy!