Broccoli Cheddar Grilled Cheese

medium yellow onion (, chopped)

large head of broccoli (, chopped well (if you don't want to use the stems, you need to get more florets))

butter

slices sharp cheddar cheese ((you can use any variety of cheddar))

garlic clove (, diced)

salt and pepper

slices fresh bread ((I like a rustic type of bread, sourdough or french are great))