To prepare lemon simple syrup: Bring ½ cup sugar and ½ cup water to a simmer in a small saucepan over medium heat, stirring occasionally until the sugar dissolves. Stir in lemon zest and remove from heat. Cover and let steep for 1 hour, then strain the syrup through a fine-mesh sieve; discard the zest. (You'll have extra syrup; refrigerate for up to 1 week.)
To prepare whipped lemonade: Add ½ cup simple syrup, ½ cup lemon juice, 1 cup coconut milk and 2 ½ cups ice to a blender. Blend until the ice is crushed and the mixture is slushy. Divide between 4 8-ounce glasses and serve immediately.
