Wash and dry all produce. Halve, peel, and thinly slice onion. Core and finely chop tomato. Remove and discard tough stems and ribs from kale; roughly chop leaves. Chop garlic. Cut potatoes into 1-inch cubes and place in a medium pot with enough water to cover by 2 inches.

Bring potatoes to a boil. Cook until tender, about 15 minutes. Reserve 1/2 cup cooking water, then drain and return to pot. Mash to desired consistency. Stir in Parmesan, sour cream, and 1 TBSP butter. (TIP: If needed, add cooking water 1-2 TBSP at a time to create a creamy consistency.) Season with salt and pepper. Cover pot and set aside.

Meanwhile, heat another 1 TBSP butter and a drizzle of olive oil in a medium pan over medium heat (we used nonstick). Add onion, 1/2 tsp sugar, and a pinch of salt and pepper. Cook, tossing occasionally, until softened, about 10 minutes. Increase heat to medium high. Stir in tomato, vinegar, and 1/3 cup tap water. Cook until jammy, 3-5 minutes. Season with salt and pepper; set aside.

While onion cooks, pat chicken dry with a paper towel. Season all over with plenty of salt and pepper. Heat a large drizzle of olive oil in a large pan over medium-high heat. Add chicken and cook until no longer pink in center, 6-8 minutes per side. Transfer to pan with onion jam. Keep covered off heat until ready to serve.

Place kale and 1 TBSP tap water in a large microwave-safe bowl. Cover bowl with plastic wrap. Microwave on high until tender, about 3 minutes. Carefully remove wrap. Heat a drizzle of olive oil in large pan used for chicken over medium-high heat. Add garlic and cook until fragrant, about 30 seconds. Toss in kale and any liquid in bowl. Cook until liquid evaporates, 1-2 minutes.

Season kale with salt and pepper. Divide mashed potatoes, kale, and chicken between plates. Spoon onion jam over chicken and serve.