Heat olive oil and butter in a Dutch oven over medium. Add onion, celery, carrots, and a pinch of salt; cook until soft and glossy. Stir in garlic and cook 30 seconds until fragrant.
Add potatoes, chicken broth, thyme, parsley, bay leaf, salt, and pepper. Bring to a gentle boil, then reduce to a lively simmer; cook 10–12 minutes until potatoes are just tender.
Stir in diced chicken and egg noodles. Simmer 6–8 minutes until chicken is cooked through and noodles are al dente; adjust salt to taste.
Whisk milk with cornstarch to make a smooth slurry. Stream into the pot while stirring; simmer 2–3 minutes until slightly thick and velvety. Remove bay leaf. Add a squeeze of lemon if desired.
Turn off heat and rest 3 minutes to settle. Garnish with parsley and cracked pepper. Serve with crusty bread or a simple salad.
Tips: Cook noodles in the soup for more flavor, or boil separately if planning leftovers to prevent sogginess. Evaporated milk adds body without heaviness.