Preparation

1. Cook spaghetti in a large pot of generously salted water over medium-high heat until al dente, about 9-10 minutes. Reserve 1 cup pasta cooking liquid. Drain spaghetti.
2. Meanwhile, preheat oven to broil with rack about 8 inches from heat. Broil poblanos and garlic on a parchment lined baking sheet until charred, 2 to 3 minutes per side for garlic and 6 to 8 minutes per side for poblanos.
3. Place charred poblanos in a paper bag and let steam for 10 minutes. Rub off and discard charred skin from poblanos. Cut poblanos in half; remove and discard seeds and stem. Remove and discard garlic skins.
4. Place poblanos, garlic, greek yogurt, scallions, jalapeno, cilantro, cumin and salt into a blender. Process until a smooth sauce forms, about 1 minute.
5. Pour poblano sauce into a large, deep skillet, and bring to a simmer over medium heat. Add butter and 1/2 cup reserved pasta water to skillet and mix well. Add cooked spaghetti. Cook, stirring constantly, until butter melts and sauce thickens enough to coat pasta, about 3 minutes, adding up to remaining 1/2 cup pasta water as needed to achieve desired sauce consistency. Season to taste with additional salt. Garnish with queso fresco and serve immediately. Tip: Charred and peeled poblanos and garlic can be stored in an airtight container in the refrigerator for up to 3 days.