The oil-and-freezer method of preservation works best with the tougher hard herbs such as rosemary, sage, thyme, and oregano. These are all herbs that would probably be cooked when added to a dish.
Soft herbs such as mint, basil, lemon verbena, and dill are usually added raw to a dish, and they don't respond as well to this kind of preserving.
8 Steps for Freezing Herbs in Oil
- Choose firm, fresh herbs, ideally from the market or your own garden.
- If you wish, you can chop them fine. Or leave them in larger sprigs and leaves. Here I froze a combination of finely-chopped and whole herbs such as rosemary, fennel stalk, sage, and oregano.
- Pack the wells of ice cube trays about 2/3 full of herbs.
- You can mix up the herbs, too; think about freezing a bouquet garni of sage, thyme, and rosemary to add to winter roast chickens and potatoes!
- Pour extra-virgin olive oil or melted, unsalted butter over the herbs.
- Cover lightly with plastic wrap and freeze overnight.
- Remove the frozen cubes and store in freezer containers or small bags.
- Don't forget to label each container or bag with the type of herb (and oil) inside!
source: The Kitchn