Cut basil leaves from the branch with gardening shears. Wash the basil leaves under cold water. Dry the leaves between paper towels.
Preheat your oven to 140 degrees Fahrenheit. Allow the oven to warm at this temperature for 20 minutes. Spread basil leaves out in a single layer on a baking sheet. Turn the oven off, and place the baking sheet in the oven. Drying basil at a warm temperature versus a high one allows the herb to retain more flavor.
Turn your oven light on to watch the basil as it dries. Warm the basil for 15 to 20 minutes until it crumbles, checking it throughout the warming time to prevent browning because browned herbs give off a burnt flavor. Remove the baking sheet from the oven.
Crush dried basil with a mortar and pestle, if desired. Store crushed or whole dried basil in an airtight container in a cool, dry place such as a kitchen pantry that does not receive direct sunlight.