I don't consider my kitchen/pantry "stocked" unless I have a jar of roasted garlic around. I do mine in oil, so you get both products when you're done. Fill small mason jars with whole, peeled garlic cloves and cover with canola oil, then into canning rack in the pressure cooker for about 45 minutes, with the jar lids on, just like you'd can veggies. Jars keep in the pantry for months. I load up at CostCo (3# bags of garlic - oh yeah, baby!) and do a batch about twice a year. They make nice Christmas presents, too!
When I open a jar, I separate out the oil into a small bottle and used as a finishing/flavoring oil. I toss the roasted garlic cloves into the food processor and pulse into a smooth paste. Back into the jar and cover with some fresh oil. Will keep in the fridge for weeks.
Like CC said, I can't imagine mashed potatoes without a big spoonful of roasted garlic paste in them!