
Add the poblano peppers to a baking sheet and place under the broiler for 10 minutes until the skin is blackened and blistered, flipping halfway through.
Remove the baking sheet from the broiler and cover it with aluminum foil or plastic wrap. Let it sit for 10 minutes. Uncover and remove as much of the skin from the peppers as possible.
Make a vertical slit down one side of the peppers and remove the seeds and veins.
Transfer the roasted poblanos to a blender and add the sour cream, cilantro, garlic, milk, lime juice, and salt. Blend until smooth. Taste and add more salt if needed.