I like to slice 6 onions in the food processor and cook them with butter in a skillet over medium heat with salt and pepper.  I cook them for at least 30-40 minutes stirring occasionally until they are nice and golden brown and very caramelized.  I let them cool and then put them in baggies and freeze them.  I add them to mashed potatoes, frittatas, put between chicken breasts with sage and fontina cheese, wrap them with prosciutto and bake, and use them as a garnish and whatever else I can think of.  I love caramelized onions!