Wash basil leaves gently and pat completely dry. Remove leaves from stems. Large leaves can be left whole or roughly chopped.
Oil cube method (best for cooking): Pack basil leaves into ice cube tray compartments, filling about ⅔ full. Pour olive oil over the leaves to fill the compartment. Freeze solid, pop out cubes, and transfer to a freezer bag. Each cube is roughly 1 tablespoon of basil-infused oil — drop directly into pasta, sauces, or soups.
Purée method (best for pesto): Blend basil leaves with just enough olive oil to make a smooth paste. Freeze in ice cube trays, then bag. When ready to make pesto, thaw cubes and add garlic, pine nuts, Parmesan, and additional oil.
Whole-leaf flash freeze: Lay individual dry leaves on a parchment-lined sheet pan. Freeze flat, then carefully transfer to a container (not a bag — frozen leaves shatter easily). This method is useful if you want to crumble frozen basil directly into dishes.
3 to 6 months.
For cooking: use directly from frozen. Drop oil cubes into hot pans or simmering sauces. For pesto: thaw cubes in the refrigerator.