Cook the Pasta: Bring a large pot of salted water to a boil. Cook the fettuccine until al dente according to the package instructions. Reserve some pasta water before draining.

Prepare the Sauce:

In a large skillet or Dutch oven, melt the butter over low heat.

Stir in the chile crisp one tablespoon at a time, tasting as you go to achieve your desired spice level. The solids in chile crisp add the most flavor, so focus on incorporating those.

Whisk in the heavy cream and keep the sauce warm over low heat. Avoid boiling.

Combine Pasta and Sauce:

Use tongs to transfer the cooked pasta to the sauce, allowing some of the residual water to mix in.

Add the spinach and toss until wilted and well-coated with the sauce.

Sprinkle in the Parmesan and toss again, adding small amounts of reserved pasta water to achieve a creamy consistency.

Serve: Divide the pasta among serving bowls. Top with additional Parmesan and chile crisp for garnish. Serve immediately.