Use a mortar and pestle to mash the mint leaves you can add a little sugar to help break up the leaves and get the oils from the mint extracted.

Remove and discard the rind and seeds of the watermelon. Place the watermelon, rum, simple syrup and lime juice in a blender and blend until smooth. Stir to get the froth to go down.

Put the mashed mint into a large pitcher and add in the watermelon mixture. Stir to combine the mint with the juice.

Place ice cubes in 6 glasses and pour the mojito mixture into the glasses. Garnish with sprigs of fresh mint and spears of watermelon.