Homemade Marshmallows

• About 1 cup powdered sugar
• 3 tablespoons unflavored gelatin, about 3 1/2 envelopes
• 1 cup cold water, divided
• 2 cups granulated sugar
• 1/2 cup brown rice syrup (or an additional 1 cup sugar and 1/4 cup water)
• 1/4 teaspoon salt
• 2 large egg whites
• 1 vanilla bean, scraped or 1 tablespoon vanilla

 Grease the bottom and sides of a square-edge 9×13 rectangular pan with butter or flavorless cooking oil. Generously dust the sides and bottom of the pan with powdered sugar. Set aside. Pour half a cup of cold water in the bowl of a standing mixer. (The marshmallows can also be made in a large mixing bowl with a hand mixer, but it will likely double the times involved.) Sprinkle the gelatin over the water and let stand to soften.
In a heavy saucepan, combine the sugar, syrup, 1/2 cup cold water and the salt. Cook over low heat, stirring occasionally with a wooden spoon, until the sugar is dissolved. Increase the heat to medium and boil the mixture until a candy thermometer registers 240 degrees, about 12 minutes. Remove from the heat and pour the sugar mixture over the gelatin, stirring until the gelatin has dissolved.