In a medium bowl, combine fresh lemon slices, granulated sugar, fresh mint leaves, chopped rosemary, and vanilla seeds. Gently massage the mixture for about 2-3 minutes until the sugar dissolves and the herbs become aromatic.

Cover the bowl with plastic wrap and refrigerate for 3-4 hours, or ideally overnight.

Set a fine-mesh strainer over another bowl or large measuring cup. Pour the infused mixture into the strainer and press down on the solids to extract every drop of juice.

Discard any remaining solids in the strainer.

In a large pitcher, combine the freshly extracted juice with 8 cups of cold water. Stir thoroughly to ensure they are well blended.

Taste the mixture and adjust sweetness by adding more sugar or a natural sweetener if desired.

Fill glasses with ice cubes and pour the lemonade over them, allowing it to chill quickly.

Garnish each glass with fresh mint or rosemary sprigs and a slice of lemon.