Whisk the sour cream, milk, minced cilantro, lime zest, and lime juice together in a small bowl until smooth. Season with salt and pepper to taste, then cover and refrigerate until needed.

Adjust an oven rack to the highest position, about 6 inches from the broiler element, and heat the broiler. Line a broiler pan or baking sheet with foil and arrange the flattened peppers skin-side up. Broil until the skins are charred and puffed, about 10 to 15 minutes, rotating the pan as needed.

Transfer the charred peppers to a large bowl and cover tightly with plastic wrap. Let the peppers steam for 15 minutes to loosen the skins, then peel the peppers and discard the skins.

Heat the olive oil in a Dutch oven over medium heat. Add the onion and cook until softened and translucent, about 5 to 7 minutes. Stir in the garlic, cumin, paprika, tomato paste, and flour; cook until fragrant and the tomato paste begins to darken, about 1 minute.

Slowly whisk in the vegetable broth, scraping up any browned bits from the bottom of the pot. Add the roasted peppers and the bay leaf. Bring to a simmer, then reduce the heat to low and cook until the peppers are very tender, about 15 to 20 minutes.

Remove and discard the bay leaf. Working in batches, puree the soup in a blender until completely smooth. Return the soup to the pot and stir in the half-and-half and sherry. Warm through over low heat without letting it come to a boil.

Adjust the consistency with extra broth if needed and season with salt and pepper. Stir in the fresh cilantro and serve hot, topped with a dollop of the chilled cilantro cream.