Bring a large pot of salted water to a boil. Add dry spaghetti and cook until al dente, about 8–10 minutes. Reserve a cup of pasta water, drain spaghetti, and return to pot to keep warm.

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add diced onion and chopped jalapeño, sauté for about 3 minutes until translucent. Stir in minced garlic and baby spinach, cooking for another 2 minutes until spinach is wilted and garlic is fragrant.

Transfer sautéed vegetables to a blender. Add roasted poblano peppers, fresh cilantro, sour cream, bouillon granules, and milk. Blend until smooth and creamy, about 1–2 minutes.

Pour blended sauce back into the pot with spaghetti. Stir in cream cheese, allowing it to melt on low heat. Mix everything, ensuring spaghetti is well coated.

Dish out creamy spaghetti onto plates, garnishing with cilantro and optional toppings like crumbled cheese or pepitas.