Preheat your oven to 350 degrees Fahrenheit.
Slice the poblano peppers in half lengthwise.
Remove the seeds and stems.
Place the peppers on a baking sheet and roast for 20-30 minutes, until the skins char and bubble.
While the peppers are roasting, heat olive oil in a pan over medium heat.
Add chopped onion and garlic.
Cook until the onions are translucent and garlic is fragrant.
Once the peppers are done, let them cool slightly.
Peel off the charred skins.
Add the roasted peppers, cooked onion, and garlic to a blender.
Pour in the chicken broth and heavy cream.
Blend until smooth.
Pour the blender mixture back into the pan on medium-low heat.
Stir in sour cream, cumin, salt, and black pepper.
Continue to stir until the sauce thickens to your desired consistency.