Peel the parsnips. Cut parsnips down the center, lengthwise. Then cut each half into 3 to 4 pieces, about 1/2 inch to 1-inch wide and about 4 inches long. You can cut away the woody core, if desired.
On a rimmed baking sheet, toss parsnips with oil, rosemary and garlic, then season with salt and pepper.
Roast until tender and golden, about 25 to 30 minutes, stirring once halfway through. You should be able to easily pierce them with a fork.
Storing: Store in an airtight container or bag in the fridge for 4-5 days. Freezing: Cooked and cooled roasted parsnips can be frozen by adding them to a baking sheet in a single layer, freezing them completely, then adding them to a freezer-safe bag. They will last 3 months. Thaw overnight in the fridge before reheating and serving.