Rinse basil leaves and gently pat dry with a towel.
Pulse basil leaves in a food processor until they are as small as you can get them. Don't worry if there are still some big pieces since you'll process them further in a bit. You should end up with about one packed tablespoon of chopped up basil. Add more basil or remove some if you are too far off.
Place processed basil and sugar in a small bowl and use a spoon to mix well, pressing the basil into the sugar.
Place the basil sugar in the food processor and pulse to fully combine.
If not using within three days, store in the freezer until ready to use.
If basil sugar starts to get clumpy, pulse again in a food processor just before using.
You can follow these same instructions with powdered sugar for use in basil frosting!Yield 1 cup