Roasted balsamic onions

I often find myself in a situation where I only need a few tablespoons of onion for a recipe to feed the two of us. What do you do with the other 80% of the onion? I've tried storing them double wrapped in the fridge, but it's nearly impossible to fully contain the smell. I've taken to roasting the remaining onion with olive oil, balsamic vinegar, salt and pepper. The onions take on a caramelized flavor and can be stored in the fridge without any ill effect. Plus they're great on salads, pasta and pizza.

Cut an onion in half lengthwise. Cut each half into 1/4 inch slices. Toss with about a teaspoon of olive oil, a teaspoon of balsamic vinegar and salt and pepper to taste. Roast at 375 degrees for about 15 - 20 minutes, stirring occasionally. After the onions are tender, remove from oven and toss with another teaspoon of balsamic vinegar. You can easily double or triple this recipe to make as many as you need.

These are great to make in advance. We had them tonight on a bed of arugula with gorgonzola and dried cranberries.