Place the tomatillos, white onion, poblano pepper, jalapeno, and garlic on a parchment-lined baking sheet. Broil for 12-15 minutes until the vegetables are tender and slightly charred.
Use a food processor to combine the tomatillos, white onion, peppers, garlic, and fire roasted tomatoes. Once blended, add the sour cream, flour, and salt. Pulse until smooth.