Add the lemong juice and zest to a bowl, then pour in 300 ml (approximately 10 ounces). Cover, and chill overnight. Bring the sugar to a boil in a saucepan with 300 ml (approximately 10 ounces) water, and simmer over low heat for 10 minutes until syrupy. Cool slightly. Pass the lemon juice mixture through a strainer into a bowl. Add the sugar syrup, mix well, and transfer to a decanter. Chill until ready to serve.
Add ice cubes (to taste) and the sliced lemon to the lemonade. Serve garnished with herbs.