1. Boil Potatoes
Preheat oven to 450 degrees. Rinse all produce. Quarter potatoes, place in medium pot, and cover with cold water by 1 inch. Season generously with salt and bring to a boil over high heat. Cook until tender when pierced with a knife, 9-10 minutes. Reserve 1/4 cup potato cooking water, then drain and return to pot, off heat. Cover to keep warm.
2. Make Garlic-Thyme Oil
While potatoes boil, mince thyme and crush garlic cloves. In a small bowl, stir together thyme, garlic, and 1 tablespoon olive oil; set aside. Pat chicken very dry with paper towel, season all over with salt and pepper. Heat 2 teaspoons olive oil in medium pan over medium-high heat.
3. Cook Chicken
When oil in pan is shimmering, add chicken. Sear for about 6 minutes. Flip chicken, pour over garlic-thyme oil, and continue cooking, repeatedly spooning garlic-thyme oil over chicken, until cooked through, about 6 minutes more. Remove pan from heat. Transfer chicken and garlic to cutting board and set aside to rest.
4. Roast Kale
While chicken cooks, pat kale dry with paper towel and tear leaves into bite size pieces. On a baking sheet, toss kale with 1 tablespoon olive oil to coat. Arrange in a single layer, roast until kale is crisp and lightly browned, 5-10 minutes.
5. Mash Potatoes
While kale roasts, scrape over garlic using a large knife, pressing down. Repeat until garlic is broken down and a paste forms. To pot with potatoes, add butter, buttermilk, garlic paste, and reserved potato cooking water. Mash until smooth. Season with salt and pepper as desired.
6. Plate Chicken
Once kale is crisp, toss on baking sheet with salt. Cut rested chicken into 1/4-inch slices. Divide mashed potatoes, chicken, and kale between serving plates. Dig in!