Zest and juice the Meyer lemon (approximately 3 tablespoons of juice).

Chop and toast the hazelnuts until golden brown.

Wash and chop the fresh spinach.

In a bowl, combine the lemon zest, lemon juice, mascarpone cheese, salt, fresh pepper, and nutmeg.

Whisk the ingredients together until smooth and well combined.

Bring a pot of salted water to a boil.

Cook the spaghetti until al dente, removing it from the heat 1-2 minutes before fully cooked.

Reserve about 1/2 cup of the pasta water before draining the pasta.

Return the drained pasta to the pot and set over low heat.

Stir in the mascarpone sauce, coating the pasta evenly.

Add the chopped spinach to the pot and toss until the spinach begins to wilt.

Add about 1/4 cup of the reserved pasta water (or more if needed) to maintain a fluid, but not watery sauce.

Continue to cook and toss until the spinach is fully cooked and tender.

Add the toasted hazelnuts to the pot and stir to combine thoroughly.

Serve the pasta immediately while it is hot and creamy.