Adjust rack to top position and preheat oven to 400 degrees. Bring a medium pot of salted water to a boil. Wash and dry produce.

Halve bell pepper; remove stem and seeds. Trim and thinly slice scallions, separating whites from greens.

Drizzle bell pepper halves with olive oil and season with salt and pepper; arrange cut sides down on a lightly oiled baking sheet.

Peel garlic; place clove in the center of a small piece of foil; drizzle with oil and season with salt and pepper. Cinch into a packet and place on same sheet.

Roast on top rack until bell pepper is lightly charred and garlic is softened, 20-25 minutes.

Once bell pepper and garlic have roasted 15 minutes, add agnolotti to pot of boiling water; reduce to a low simmer. Cook, stirring occasionally, until al dente and floating to the top, 3-5 minutes.

Reserve ½ cup pasta cooking water (1 cup for 4 servings), then drain and set aside. Keep empty pot handy for Step 5.

Once bell pepper and garlic are done roasting, carefully transfer to a cutting board. Thinly slice bell pepper and gently mash garlic with a fork until smooth.

Heat a drizzle of olive oil in pot used for pasta over medium-high heat. Add scallion whites; cook, stirring occasionally, until fragrant, 1 minute.

Add ¼ cup reserved pasta cooking water (⅓ cup for 4 servings), stock concentrate, cream cheese, sour cream, half the Parmesan, and 1 TBSP butter (2 TBSP for 4); stir until smooth.

Stir in bell pepper and mashed garlic. Bring to a simmer and cook until slightly thickened, 1-2 minutes. Turn off heat. Season with salt and pepper.

Stir agnolotti into pan with sauce. TIP: If needed, stir in more reserved pasta cooking water a splash at a time until pasta is coated in a creamy sauce.

Divide between bowls. Season with pepper. Garnish with scallion greens and remaining Parmesan. Serve.