Pour the white wine into a saucepan and heat over medium heat until steaming hot (around 65-70°C / 150-160°F), about 3-5 minutes, without bringing to a boil.
Stir in the elderflower syrup and add 1 slice of lemon.
Pour the hot wine mixture into mulled wine cups.
Garnish each cup with a lemon slice and a few fresh peppermint leaves.