Adjust rack to top position and preheat oven to 425 degrees. Bring a large pot of salted water to a boil. Wash and dry produce.

Trim and discard woody bottom ends from asparagus; cut stalks crosswise into 1-inch pieces. Mince garlic. Zest and quarter lemon.

Toss asparagus on a baking sheet with a drizzle of oil, salt, and pepper. Roast on top rack until tender and lightly browned, 10-12 minutes.

Once water is boiling, add spaghetti to pot. Cook, stirring occasionally, until al dente, 9-11 minutes. Reserve 1 cup pasta cooking water (2 cups for 4 servings), then drain.

Return spaghetti to pot and set aside.

Place scallops* in a strainer and rinse under cold water to remove any grit. Gently remove any small side muscles if necessary and pat dry with paper towels. Season with salt and pepper. Heat a large drizzle of oil in a large, preferably nonstick, pan over medium-high heat.

Once pan is very hot, add scallops; cook, undisturbed, until lightly browned on bottoms, 2-3 minutes. Flip scallops and stir in 1 TBSP butter (2 TBSP for 4 servings) until melted. Cook, spooning butter over scallops, until scallops are opaque and cooked through, 1-2 minutes more. Turn off heat; transfer to a plate and tent with foil. Wipe out pan and let cool slightly.

Heat a drizzle of oil in pan used for scallops over medium-high heat. Add garlic; cook, stirring, until fragrant, 30 seconds.

Whisk in cream sauce base, stock concentrate, and ⅓ cup reserved pasta cooking water (¾ cup for 4 servings). Cook, whisking, until slightly thickened, 2-4 minutes.

Reduce heat to medium low and whisk in sour cream until smooth.

Transfer sauce to pot with drained spaghetti; add roasted asparagus, Parmesan, 1 TBSP butter (2 TBSP for 4 servings), a big squeeze of lemon juice, and a pinch of lemon zest.

Reduce heat to low. Cook, stirring, until butter has melted and everything is coated in a creamy sauce. TIP: If needed, stir in more reserved pasta cooking water a splash at a time.

Divide pasta between shallow bowls. Top with scallops and a squeeze of lemon juice just before serving.