This is a Martha Stewart recipe and they're so much better than the ones you buy. My friend Tiffany puts peppermint extract in hers and swirls red food coloring in it after pouring them, but I haven't tried that yet. If any of you do, let me know how they turn out!
2 1/2 tbsp Knox unflavored gelatin (about 3 envelopes)
1 1/2 cups sugar
1 cup light corn syrup
1/4 teaspoon salt
2 tablespoons vanilla
Confectioners' sugar, for dusting
Combine gelatin and 1/2 cup cold water in the bowl of an electric mixer with whisk attachment. Let stand 30 minutes.
Combine sugar, corn syrup, salt, and 1/2 cup water in a small heavy saucepan; place over low heat, and stir until sugar has dissolved. Wash down sides of pan with a wet pastry brush to dissolve sugar crystals.
Clip on a candy thermometer; raise heat to high. Cook syrup without stirring until it reaches 244 degrees(firm-ball stage). Immediately remove pan from heat.
With mixer on low speed, slowly and carefully pour syrup into the softened gelatin. Increase speed to high; beat until mixture is very thick and white and has almost tripled in volume, about 15 minutes. Add vanilla; beat to incorporate.
Generously dust an 8-by-12-inch glass baking pan with confectioners’ sugar. Pour marshmallow mixture into pan. Dust top with confectioners’ sugar; wet your hands, and pat it to smooth. Dust with confectioners’ sugar; let stand overnight, uncovered, to dry out. Turn out onto a board; cut marshmallows with a dry hot knife into 1 1/2-inch squares, and dust with more confectioners' sugar. Makes about 40 marshmallows.