This is a great sauce to make ahead, divide into portions and stash in the freezer. Whenever you want to add a little Mexican-style flavor and flair to simply cooked chicken, pork or steak, heat up one portion, drizzle it on top and you're good to go! (Rach loves the creamy sauce on eggs, too!)
Preheat broiler to high.
With the oven door ajar to allow steam to escape, broil the poblanos until charred all over. Place chiles in a bowl, cover with plastic wrap and let cool. Peel, seed and roughly chop.
Melt butter in a large skillet over medium-high heat. Add onions, garlic and cumin and season with salt and pepper. Cook until onions are translucent, 8 to 10 minutes.
Add poblanos, then whisk in flour and cook for 1 to 2 minutes. Add stock and let thicken.
Transfer to a food processor, add cilantro and puree. Transfer to a pot, add cream and let thicken to coat a spoon.
Freeze flat in a resealable gallon-size bag or in sandwich-size bags for smaller servings.
Serve over chicken, pork or steak.