In a large bowl of an electric mixer add 3 egg whites and 1/2 teaspoon cream of tartar. Add the beater attachment and plug in the mixer so it’s ready to go.
In a medium saucepan, combine 3/4 cup sugar, 3/4 cup karo syrup and 1/3 cup water over medium heat. Bring to a boil and stir constantly. Clip a candy thermometer to the pan.
While the sugar mixture is cooking, start whipping the egg whites in the mixing bowl until they become foamy.
Once the candy mixture reaches 240°F, drizzle the mixture SLOWLY into the bowl with the egg whites. Scrape down the sides and then beat on high speed until the the mixture has doubled and a soft peak forms (about 5 minutes). When mixture becomes fluffy and shiny you know it's ready. Add 1 teaspoon vanilla and beat an additional minute.
Store in a covered container at room temperature for 2 weeks. Serve as a topping on top of desserts or use as a replacement for jarred marshmallow fluff in baked goods.
Notes
Storage: Store in a mason jar at room temperature for up to 4 weeks. Do not freeze, it separates upon thawing.S'mores bites: Leftover fluff? Spread between 2 pieces of graham crackers and them dip in melted chocolate. Makes the ultimate gooey s'mores bite.