Martha Stewarts Marshmallows

Recipe adapted from Martha Stewart

Ingredients

Vegetable oil, (for brushing baking dish)
4 envelopes unflavored gelatin
3 cups sugar
1 1/4 cups light corn syrup
1/4 teaspoon salt
2 teaspoons vanilla extract
3/4 cups powdered sugar

Directions

Brush a 9-by-13-in. glass baking dish with oil. Line with parchment, making sure you have a 2-inch overhang on the long sides. Brush parchment with oil; set aside.

1. Put sugar, corn syrup, salt, and 3/4 cup water into a medium saucepan. Bring to a boil over high heat, stirring until sugar is dissolved. Cook, without stirring, until mixture registers 238 degrees on candy thermometer about 9 minutes.
2. Meanwhile, put 3/4 cup cold water into the bowl of an electric mixer; sprinkle with gelatin. Let soften 5 minutes.
3. Using the whisk attachment in the bowl with gelatin mix on low speed, beat hot syrup into gelatin mixture. Gradually raise speed to high; beat until mixture is very stiff, about 12 minutes. Beat in vanilla. Pour into prepared dish, and smooth with an offset spatula. Set aside, uncovered, until firm, about 3 hours.
4. Sift 3/4 cup confectioners' sugar onto a work surface. Unmold marshmallow onto confectioners' sugar; remove parchment. Lightly brush a sharp knife with oil, then cut marshmallow into 2-inch squares.

Marshmallows can be stored in an airtight container up to 3 days.