Adjust rack to middle position and preheat oven to 425 degrees. Wash and dry all produce. Dice potatoes into 1-inch pieces. Mince half the garlic (keep the remaining whole). Thinly slice chives. Peel and cut carrots on a diagonal into 1/2-inch-thick pieces. Zest and quarter lemon (quarter both lemons for 4 servings); squeeze 1 TBSP juice (2 TBSP for 4) into a small bowl.

Place potatoes and whole garlic clove in a medium pot with enough salted water to cover by 2 inches. Bring to a boil; cook until tender, 15-20 minutes. Reserve 1/2 cup potato cooking liquid; drain. Return potatoes and garlic to pot; add sour cream and 1 TBSP butter (2 TBSP for 4). Mash, adding splashes of reserved cooking liquid as needed, until smooth. Add half the chives, salt, and pepper. Cover to keep warm.

While potatoes cook, toss carrots on a baking sheet with a drizzle of olive oil, salt, and pepper. Roast on middle rack until lightly browned and tender, 20-25 minutes. Remove from oven and toss with half the lemon zest.

Meanwhile, reserve 1/2 tsp flour (we’ll use it later; 1 tsp for 4 servings). Combine remaining flour, half the Tuscan Heat Spice (use all for 4), salt, and pepper on a plate. Pat chicken dry with paper towels; season all over with salt and pepper. Using tongs, coat both sides of chicken in flour mixture.

Heat a large drizzle of olive oil in a large, preferably nonstick, pan over medium-high heat. Add chicken (tapping off any excess flour); cook until browned on first side, 3-5 minutes. Flip and add another large drizzle of olive oil to pan. Cook until browned and cooked through, 3-5 minutes more. (TIP: If browning too quickly, reduce heat.) Transfer to a plate. Heat a drizzle of olive oil in same pan over medium heat. Add minced garlic, reserved flour, and remaining lemon zest. Cook until fragrant, 20-30 seconds. Add stock concentrate, 1/4 cup water (1/3 cup for 4), lemon juice, salt, and pepper. Simmer until thickened, 1-2 minutes. Turn off heat.

Heat a drizzle of olive oil in same pan over medium heat. Add minced garlic and remaining flour and lemon zest. Cook until fragrant, 20-30 seconds. Add stock concentrate, 1/4 cup water (1/3 cup for 4), reserved lemon juice, salt, and pepper. Simmer until thickened, 1-2 minutes. Turn off heat; stir in 1 TBSP butter (2 TBSP for 4). Divide chicken, potatoes, and carrots between plates. Top chicken with sauce. Garnish with remaining chives. Serve with any remaining lemon wedges on the side.