Fill a large pot with salted water and bring to a rolling boil. Add pasta and cook until al dente, about 8–10 minutes.

In a large skillet, melt butter with olive oil over medium heat. Add garlic and cook until fragrant, about 1–2 minutes.

Stir in fresh spinach leaves, tossing gently for 1–2 minutes until they turn bright green and just wilted.

Drain pasta, reserving ½ cup pasta water. Add pasta to the skillet, tossing with sauce. Stir in reserved water for a silky texture.

Season with salt and pepper to taste. Remove from heat, divide among plates, and sprinkle with freshly grated Parmesan and red pepper flakes.