Roast the Poblano Peppers
Place the poblano peppers over an open flame or under a broiler, turning them until all sides are charred and blistered. Once charred, place the peppers in a sealed plastic bag or cover them with a bowl to steam for about 10 minutes. This will make peeling easier. After steaming, peel off the charred skin, remove the stems and seeds, and set the peppers aside.

Cook the Spaghetti
In a large pot, bring salted water to a boil. Add the spaghetti and cook according to the package instructions until al dente. Reserve about a cup of the pasta cooking water, then drain the spaghetti and set aside.

Prepare the Poblano Sauce
In a blender, combine the roasted poblano peppers, cilantro, chopped onion, garlic, Mexican crema, cream cheese, chicken bouillon cube, and ½ cup of milk or reserved pasta water. Blend until smooth. If the sauce seems too thick, add more milk or pasta water to achieve the desired consistency.

Cook the Sauce
In a large skillet, melt the butter or heat the olive oil over medium heat. Pour in the blended poblano sauce and bring it to a gentle simmer. Season with salt and freshly ground black pepper to taste.

Combine Pasta and Sauce
Add the cooked spaghetti to the skillet with the sauce. Toss well to ensure the pasta is evenly coated with the sauce. If the mixture is too thick, add a bit more milk or pasta water to loosen it up.

Serve
Transfer the green spaghetti to serving plates and garnish with crumbled Cotija cheese and additional cilantro if desired. Serve immediately.