Place the poblano peppers on a baking sheet and broil in the oven until the skins are blackened and blistered. Turn half way so both sides get blackened, about 10 minutes total. Check on the peppers frequently.
Remove the peppers from the oven and place them in a bowl and cover with plastic wrap. Allow the peppers to steam for 10 minutes. Remove the stem and seeds and chop into smaller pieces.
Place the peppers in a food processor and pulse a few times.
Add the mayonnaise, Greek yogurt, milk, cilantro, garlic, lime juice, smoked paprika and Ranch seasoning and blend until mostly smooth. Adjust the flavor with salt and pepper to your taste.
For the best flavor, cover and refrigerate the dressing for at least 1 hour before serving to allow the flavors to develop more.