Adjust rack to top position and preheat oven to 450 degrees. Wash and dry produce.

Dice potatoes into ½-inch pieces. Halve and peel onion; grate one half on the largest holes of a box grater. Thinly slice remaining onion.

Place potatoes in a medium pot with enough salted water to cover by 2 inches. Bring to a boil and cook until tender, 15-20 minutes. Reserve ½ cup potato cooking liquid (¾ cup for 4 servings), then drain.

Return potatoes to pot and mash with half the sour cream (you’ll use the rest later) and 2 TBSP butter (4 TBSP for 4) until smooth and creamy, adding splashes of reserved potato cooking liquid as needed. Season with salt and pepper.

Keep covered off heat until ready to serve.

Trim green beans if necessary.

While potatoes cook, in a large bowl, combine beef*, grated onion, panko, garlic powder, ¼ tsp nutmeg (½ tsp for 4 servings), salt (we used ¾ tsp, 1½ tsp for 4), and pepper. (You’ll use more nutmeg later.)

Form mixture into 10-12 1½-inch meatballs (20-24 for 4) and place on a lightly oiled baking sheet.

Roast on top rack until browned and cooked through, 14-16 minutes.

Meanwhile, melt 1 TBSP butter in a large pan over medium-high heat. Add peas and cook, undisturbed, until lightly browned, 2-3 minutes.

Stir peas. Cook, stirring occasionally, until lightly charred, 1-2 minutes more.

Turn off heat; transfer to a plate. Wipe out pan.

Swap in green beans for peas. Cook, undisturbed, until lightly browned, 3-4 minutes. Stir green beans. Cook, stirring occasionally, until lightly charred, 1-2 minutes more. (TIP: If green beans haven’t softened, stir in 1-2 TBSP water and cook a bit more.)

Heat a drizzle of oil in same pan over medium heat. Add sliced onion and a pinch of salt; cook, stirring occasionally, until onion is browned and softened, 3-6 minutes.

Add 1 TBSP butter (2 TBSP for 4 servings) and cook, whisking, until butter melts.

Sprinkle flour over onion; cook, whisking constantly, until lightly browned, 1-2 minutes.

Slowly whisk 1 cup water (1½ cups for 4 servings) into pan with onion. Add stock concentrates, cream cheese, and ¼ tsp nutmeg (½ tsp for 4); whisk until cream cheese melts and gravy has thickened, 3-5 minutes.

Remove from heat and whisk in remaining sour cream. Taste and season with salt and pepper. TIP: If gravy seems too thick, stir in a few splashes of reserved potato cooking liquid.

Add meatballs to pan with gravy; toss to coat.

Divide mashed potatoes and meatballs and gravy between bowls. Top meatballs with peas and serve.