In a medium to large pot, bring water to a boil. Add 2 broken celery sticks, Bay leaf, clove and one small onion, quartered (you can leave the onion skin on!). Add chicken breasts and keep at a low simmer until cooked through, about 20 minutes. Remove chicken and cut into 1/2" pieces, reserve.

Remove onion pieces, celery and Bay leaf; top up the water and return to a boil. Add egg noodles. Cook according to the package instructions, leaving them a bit more to the al dente side (undercook by 1 min so the bite is just slightly chewy). Drain into a colander and reserve. Add a pat of butter and stir, to prevent the noodles sticking.

Melt 3 tbsp butter in a large skillet on medium-high heat. Add onion and cook for 3–4 minutes until softened. Add garlic, celery and mushrooms. Cook until vegetables are tender and most of liquid has evapourated. 

Sprinkle with flour and cook 1–2 minutes, stirring once or twice. Add milk, salt, pepper, nutmeg and Maggi; cook gently, stirring on medium heat until small bubbles start to form. 

Add cream cheese in pieces to the skillet. Cook until cream cheese has melted and incorporated into the sauce. 

Add reserved chicken and frozen peas, Stir to combine.

Combine Parmesan and breadcrumbs in a small bowl. Melt butter and add; stir to combine. Set aside until ready to assemble.

Preheat oven to 350°

Butter an 11x8" casserole dish (I prefer the slightly smaller size for deeper serving pieces and denser breadcrumbs on top, but a 9x13" dish will work, too). Add filling. Top with breadcrumb topping. Bake uncovered in a 350° oven for 30 minutes until top is browned and the saucy is bubbling deliciously. Serve.