Adjust rack to middle position and preheat oven to 425 degrees. Wash and dry produce.

Dice potatoes into ½-inch pieces. Place in a medium pot with enough salted water to cover by 2 inches. Bring to a boil and cook until tender, 10-15 minutes. Reserve ½ cup potato cooking liquid, then drain.

Return potatoes to pot and cover to keep warm. (You’ll finish the potatoes in Step 5.)

While potatoes cook, heat a drizzle of oil in a large pan over medium-high heat. Add prosciutto in a single layer; cook until browned and crispy, 2-3 minutes per side. TIP: If prosciutto starts to brown too quickly, reduce heat to medium.

Turn off heat; transfer prosciutto to a paper-towel-lined plate. Wipe out pan.

Trim and discard woody bottom ends from asparagus. Halve, peel, and mince half the shallot (all for 4 servings). Finely chop chives.

Pat chicken* dry with paper towels; season all over with half the herbes de Provence (all for 4 servings), salt, and pepper.

Heat a drizzle of oil in pan used for prosciutto over high heat. Add chicken and sear until golden brown, 2 minutes per side. Turn off heat; transfer chicken to one side of a baking sheet. Wipe out pan and let cool slightly.

Toss asparagus on empty side of sheet with a drizzle of oil, salt, and pepper.

Roast on middle rack until chicken is cooked through and asparagus is tender and lightly browned, 12-14 minutes. Transfer chicken to a cutting board.

To pot with potatoes, add sour cream and 2 TBSP butter (4 TBSP for 4 servings); mash until smooth, adding splashes of reserved potato cooking liquid as needed. Taste and season with salt and pepper if desired.

Heat 1 TBSP butter (2 TBSP for 4) and a drizzle of oil in pan used for chicken over medium heat. Add minced shallot and cook, stirring occasionally, until fragrant, 1-2 minutes.

Reduce heat to low and whisk in ¼ cup water (½ cup for 4), jam, and demi-glace. Bring to a simmer, then cook, whisking constantly, until slightly thickened, 1-2 minutes more.

Slice chicken crosswise.

Divide chicken, asparagus, and mashed potatoes between plates. Spoon pan sauce over chicken and crumble prosciutto over potatoes. Garnish everything with chives and serve.