Arrange an oven rack in the top position and heat the broiler on high. Meanwhile, place 4 halved and seeded medium poblano peppers and 1 halved and seeded medium jalapeño pepper skin-side up in a single layer. Drizzle evenly with 1 tablespoon of the olive oil and use your hands to coat the peppers evenly.

Broil, rotating the baking sheet halfway through, until the peppers are tender and the skin is mostly blistered and blackened, 10 to 12 minutes total.

Meanwhile, heat the remaining 1 tablespoon olive oil in a large skillet over medium heat until shimmering. Add ½ sliced medium yellow onion and cook until softened and beginning to brown, about 5 minutes. Scrape into a blender. Reserve the skillet; no need to clean.

Transfer the peppers to a medium heatproof bowl and cover the bowl with plastic wrap. Let sit for 10 minutes so the peppers steam and become easy to peel.

Meanwhile, bring a Dutch oven or large pot of heavily salted water to a boil over medium-high heat. Add 1 pound dried spaghetti and cook according to package directions, stirring occasionally, until al dente.

Peel and discard the skins from the peppers. Add the peppers, 8 ounces room-temperature cream cheese, 1 cup Mexican crema, ½ cup fresh cilantro, 2 peeled garlic cloves, ½ teaspoon kosher salt, and ½ teaspoon chicken bouillon powder to the blender. Blend on high speed until well-combined, about 2 minutes. It will look speckled and a little lumpy.

Transfer the sauce to the reserved skillet. Bring to a simmer over medium heat. Continue to simmer until the sauce changes in color and slightly thickens, 2 to 3 minutes. Reduce the heat to low.

When the pasta is ready, reserve 1 cup of the pasta cooking water. Drain the pasta.

Add pasta and ½ cup of the reserved pasta water to the sauce. Cook over low heat until the sauce thickens more and clings to the pasta, about 2 minutes. Toss in more pasta water a few tablespoons at a time if needed if the pasta is dry.

Remove the skillet from the heat. Garnish with fresh chopped cilantro and crumbled queso fresco cheese if desired. Serve immediately, reserving the remaining pasta water to loosen the sauce up as needed.