Grilled Sausage and Onion Panini

Let me start by saying that I just made this recipe today and I loved it so much that I had to blog about it right away! It's from my Fine Cooking magazine collection, with a few changes. I used spinach instead of arugula and I broiled the sausage instead of grilling it. The reason for broiling the sausage was simply a time saving decision. I don't have a grill (I hate saying that) so I used my grill pan which has limited space. I had to grill the bread in two batches and then grill the onions. In order to save time I had the sausage broiling in the oven in the meantime. This recipe serves 4.