Bring a large pot of salted water to a rolling boil.
Add the egg noodles and cook according to package instructions (6-8 minutes). Drain and return noodles to the pot. Toss noodles with 2 tbsp butter, season with salt and pepper, cover to keep warm, and set aside.
Season chicken medallions with salt and black pepper on both sides.
In a large skillet, heat 2 tbsp olive oil over medium-high heat. Cook chicken for 3-4 minutes per side until golden and cooked through. Remove from skillet and set aside.
In the same skillet, add 2 tbsp butter and melt over medium heat. Add mushrooms and onion, cooking for 5 minutes until mushrooms are browned and onions are softened. Add garlic, cooking for 1 minute until fragrant.
Pour in chicken broth, scraping the bottom to incorporate browned bits. Simmer for 2-3 minutes to reduce slightly.
Stir in heavy cream and optional thyme or rosemary. Simmer until sauce thickens slightly.
Return chicken to skillet, spooning sauce over it, and simmer for 5 minutes until heated through. Plate, serve and enjoy!