Broccoli and Cheese Soup

4 tablespoons olive oil
4 cloves garlic, peeled and thinly sliced
2 yellow onions, peeled and roughly diced
4 large stalks of broccoli (about 2-2 1/2 lbs) cut into small florets
8 cups vegetable (or chicken) stock
1 1/2 teaspoons salt
1/2 teaspoon freshly ground black pepper, plus more for serving
2 cups of arugula (watercress would be good, too) or more to taste
1/4-1/2 cup of Romano or another strong cheese

Heat olive oil in a large saucepan over medium heat. Add the garlic and onion and saute for about 1  2 minuts or until fragrant. Add the broccoli and cook for 4 minutes or until bright green. Add the stock, salt, and pepper. Bring to a boil, lower the heat, and cover. Cook for 10 minutes, or until the broccoli is just tender. Pour the soup into a blender and puree with the arugula until quite smooth. You could also use an immersion blender if you have one.
As always, be very careful when blending hot liquids. Start slowly and work in batches if necessary.
Pour the soup back into the pot, stir in 1/4 cup of the cheese (or more if you'd like). 
Serve with extra black pepper and sprinkle with parmesan cheese.