Heat 2 tablespoons of olive oil in a large skillet over medium-low heat. Add 1 large sliced onion and a pinch of salt, stirring occasionally. Cook for 15-20 minutes until golden brown.

Meanwhile, bring a large pot of salted water to a boil. Add 8 ounces of farfalle pasta and cook for 10-12 minutes until al dente. Reserve a cup of pasta water, then drain.

Add 8 ounces of sliced mushrooms to the skillet, increase heat to medium, and sauté for about 5 minutes until golden and tender.

Reduce heat to low, add the drained farfalle pasta to the skillet, and gently toss to combine. Then add 4 cups of fresh spinach, folding in until it wilts.

Season with salt and pepper to taste. Add a splash of reserved pasta water if desired, and cook for an additional minute. Serve warm, optionally topped with grated parmesan or toasted pine nuts.