Step 1 Place 6 tablespoons water in a 5-quart mixing bowl. Sprinkle the gelatin evenly over the water and let the mixture stand for 5 minutes. Place the bowl over a medium saucepan of gently simmering water and allow the gelatin to dissolve without stirring. This should take 3 to 5 minutes. Remove the bowl from the heat and set aside.
Step 2 In a small saucepan, combine the remaining water, the sugar and one-fourth cup corn syrup. Cook the mixture over high heat until it reaches 235 degrees on a candy thermometer. Remove the mixture from the heat and pour in the remaining corn syrup.
Step 3Immediately begin whipping the gelatin mixture, and slowly add the hot sugar mixture as you whip. Continue whipping until the marshmallow mixture is white, light and fluffy, about 15 minutes. Beat in the vanilla.
Step 4Spread the mixture into a 9-by-13-inch baking dish coated with nonstick spray. For thicker marshmallows, use a smaller pan. Cover the pan with plastic wrap and refrigerate overnight.
Step 5Using a knife or cookie cutters, cut the marshmallow layer into desired shapes and sizes. Cover a work surface with a sheet of wax paper; lightly dust the paper with one-fourth cup confectioner's sugar. As you cut out individual marshmallows, place them on the sugared wax paper. Lightly dust the tops of the marshmallows with the remaining confectioner's sugar. The marshmallows may be tightly wrapped and stored for 3 to 5 days at room temperature.