Butter, garlic, chicken, and a mountain of mashed potatoes. Sometimes a high calorie dinner is just about the basics done really, really well.
Peel and cut russet potatoes into large chunks. Place in a large pot, cover with cold water, and add 1 tsp salt. Bring to a boil over high heat, then reduce to medium-low and simmer until tender (about 20 minutes).
While potatoes cook, pat chicken thighs dry. Season both sides with 1 tsp salt and black pepper.
Heat 0.25 cup butter in a large skillet over medium heat. Add chicken thighs, skin side down (or smooth side), and sear for 5-7 minutes without moving to develop a golden crust. Flip and cook another 5-7 minutes until just cooked through. Remove chicken and set aside, keeping warm.
Lower the skillet heat. Add remaining butter and garlic (smashed or minced) and sauté for 1-2 minutes, stirring constantly, until aromatic but not browned. Return chicken to skillet, spoon garlic butter over top, and simmer for 2-3 minutes to infuse flavor.
Drain cooked potatoes well. Return to pot over low heat for 1 minute to evaporate excess moisture. Mash, adding heavy cream and milk gradually. Stir in remaining salt, black pepper, and half of the chopped parsley. Mix until smooth and fluffy.
Plate a mound of mashed potatoes, top with butter garlic chicken and pan sauce, and sprinkle with remaining parsley. Serve immediately.