The key to a rosemary infused olive oil is making an infusion. You need a good quality olive oil and an assortment of fresh rosemary sprigs. The total number will be about 20 or so. Expect to use at least one container of olive oil and many small glass bottles.
Making rosemary infused olive oil is done on the stove and will take about ten minutes. The key for an excellent result is making sure the rosemary is not getting cooked. This means making sure the stove is at the proper heat level.