Bring a large pot of salted water to rolling boil, then add pasta and cook according to package directions until al dente, approximately 9-11 minutes. Reserve 1 cup pasta water before draining completely. The starchy water helps emulsify your sauce later, so don't skip this crucial step.

While pasta cooks, combine butter and olive oil in a large skillet over medium heat. Once butter foams, add minced garlic and sauté for 90 seconds until fragrant but not browned. Burnt garlic tastes bitter, so watch timing carefully and stir constantly throughout this stage.

Pour in chicken broth and heavy cream, stirring gently to combine. Bring to gentle simmer and add salt, black pepper, garlic powder, nutmeg, and red pepper flakes. Let this cozy creamy garlic pasta sauce simmer for 3-4 minutes to meld flavors together.

Remove from heat and gradually whisk in grated parmesan cheese, stirring until completely melted and silky. If sauce seems too thick, add reserved pasta water one tablespoon at a time until reaching desired consistency. The sauce should coat the back of a spoon generously.

Add drained pasta directly to the sauce, tossing gently but thoroughly to coat every strand. Stir in fresh spinach and lemon juice, allowing spinach to wilt for exactly one minute. Taste and adjust seasoning with additional salt, pepper, or lemon juice as needed before serving immediately.