Bring a large pot of salted water to a boil. Add pasta and cook according to package instructions until al dente. Reserve some pasta water before draining.

Season steak generously with salt and pepper. Heat a skillet over medium-high heat and sear the steak until browned on both sides, about 4-5 minutes per side.

In the same skillet, reduce heat to medium-low and melt butter. Add minced garlic until fragrant, about 30 seconds, then pour in heavy cream while stirring continuously.

Stir in grated Parmesan cheese into the cream mixture until melted and smooth. Toss in fresh spinach until wilted.

Combine cooked pasta with the cream sauce. If needed, add reserved pasta water gradually until reaching desired consistency. Serve hot with extra Parmesan on top if desired.