Chop your potatoes into bite-sized pieces. If you don't have thin-skinned potatoes, you might want to peel them a little bit first but don't feel like you need to get all the peel off!
Strip the leaves off of your stalks of rosemary. You can toss the leaves in whole or give them a rough chop with a sharp knife.
Spray your baking dish with a little bit of oil. Toss the potatoes and rosemary into the pan, add the olive oil and use your fingers or 2 forks to coat the potatoes. Sprinkle a little coarse sea salt over the top.
Pop the dish into the oven preheated to 425 degrees. Let it cook for 45 to 60 minutes. After about 20 minutes or so, take a spatula or wooden spoon and stir the potatoes so that they brown evenly.
My kids don't love it when the potatoes are too crispy so I usually take mine out of the oven at around 45 minutes. Enjoy!