Place egg white, cream of tartar, and salt in a bowl. Set aside.
In a small saucepan, bring sugar, corn syrup, and raspberry puree to a boil. Let simmer until a thermometer reads 116°C (240°F). Remove from heat while you beat egg whites. Watch out for spatter.
Beat egg whites with an electric beater at medium speed until they form soft peaks. Drizzle hot syrup over egg whites, avoiding beaters. Continue beating until egg whites form firm peaks.
Pour into a jar and close tightly. Marshmallow creme will keep in the refrigerator for about a week.
Assembly
Place about 2 tbsp. marshmallow creme on each cookie and top with 2 raspberries.
Quickly brown marshmallow creme with a small kitchen torch.