Spinach Pesto Pasta

Directions

1. 1
   In a large skillet, melt butter over medium heat.
2. 2
   Add the onion and cook until caramelized, 15 - 20 minutes.
3. 3
   Bring a large pot of water to boil, salt it, add the pasta; cook al dente.
4. 4
   Drain, saving 1 cup of the pasta water.
5. 5
   While the pasta cooks heat the olive oil in a small saucepan & rosemary sprig over med-low heat & steep for 5 minutes.
6. 6
   Let it cool and discard the rosemary.
7. 7
   Pour the oil and garlic in a food processor.
8. 8
   Add the spinach and process into a thick paste.
9. 9
   Season with salt & pepper.
10. 10
    Stir the pasta cooking water into the onions, then stir in the pesto.
11. 11
    Add the cheese and toss to combine.