Place poblano peppers directly over a gas stove flame or under a broiler on high. Use tongs to turn occasionally until the skin is blackened and blistered on all sides, about 5-10 minutes.

Immediately transfer the hot peppers to a medium bowl and cover tightly with plastic wrap. Let them steam for 15 minutes. This will make the skins easy to peel.

While peppers steam, melt butter in a large pot or Dutch oven over medium heat. Add the chopped onion and cook until soft, about 5-7 minutes. Add the minced garlic and cook for 1 more minute until fragrant.

Once steamed, remove the peppers from the bowl. The blackened skins should peel off easily. Remove and discard the stems and seeds. Roughly chop the roasted pepper flesh.

Add the chopped peppers to the pot with the onions and garlic. Pour in the vegetable broth. Use an immersion blender to puree the soup until completely smooth. (Alternatively, carefully transfer to a blender and blend in batches).

Return the pot to medium-low heat. Stir in the heavy cream, cumin, and salt. Allow the soup to simmer gently (do not boil) for 10-15 minutes for the flavors to meld. Stir in the fresh cilantro and lime juice just before serving.

Ladle the hot soup into bowls and top with desired garnishes like cotija cheese, tortilla strips, or a dollop of sour cream.