Wash the lemon thoroughly, grate dry and cut into pieces. Wash basil, shake dry. Put half of the lemon cubes and 3 basil stems in a shaker and crush (muddle) them with a pestle.
Add half of the gin, add 1 1/2 tbsp. ice cubes and shake vigorously about 15 times. Put 1 tablespoon of ice cubes into a glass. Pour the gin mixture into the glass through the provided sieve of the shaker. Serve with a stalk of basil. Process remaining ingredients in the same way.