Add the chopped mint leaves, sugar, and water to a small saucepan, and bring to the boil. Stir occasionally, until the sugar has dissolved. Let simmer for 3 minutes, and then remove from the heat. Pour the syrup through a sieve to remove the mint leaves, pressing on the leaves as you do so, and let cool in a bowl or measuring cup.
Once cool, add the raspberries and Aperol to the mint simple syrup, and muddle together. Divide the mixture between 4 tall glasses. Add 2 scoops of vanilla ice cream to each glass, and then top off with seltzer.