Season the chicken thighs evenly with kosher salt and black pepper on both sides.
Heat olive oil in a large skillet over medium-high heat until shimmering.
Add the chicken thighs skin-side down and cook for 5-7 minutes until the skin is golden brown and crisp. Flip and cook for an additional 5 minutes. Remove chicken from skillet and set aside.
Reduce heat to medium and add diced onion to the skillet. Cook, stirring occasionally, until softened, about 4 minutes.
Add minced garlic and cook for 1 minute until fragrant.
Sprinkle the flour over the onions and garlic, stirring constantly to form a roux, and cook for 2 minutes to remove the raw flour taste.
Gradually whisk in the chicken broth and milk, stirring continuously to avoid lumps.
Add dried thyme, paprika, and dried sage to the skillet and stir to combine.
Bring the gravy to a simmer and add the egg noodles, stirring to submerge them in the liquid.
Return the chicken thighs to the skillet, placing them on top of the noodles skin-side up.
Cover the skillet and simmer on low heat for 15 minutes, or until the noodles are tender and the chicken is cooked through (internal temperature reaches 165°F).
Remove the lid and stir in the unsalted butter until melted and incorporated into the gravy.
Sprinkle chopped fresh parsley over the dish before serving.