Pasta with Carmelized Onion Sauce

I was a little skeptical about using this sauce on pasta, but it made for a very satisfying meal, with a nice surprise of sweet onions, small bright green bits of arugula, salty Feta cheese, and the crunch of walnuts. I used arugula instead of spinach, one of the options, and the green added great visual appeal. I used 4 very large onions and for this version of the cookbook, it used a large amount of oil, ½ cup. I wished there was a description of what the onions should have looked like at various stages of preparation “ limp, golden, brown, etc. I took a longer time to prepare this dish than I should have as I turned the temperature down too low so I could keep wandering off. This pasta dish was a delightful change from the usual tomato, cream or pesto-based sauces.