I used the Barefoot Contessa's recipe...here it is.
3 packs of unflavored gelatin
1 1/2 cups granulated sugar
1 cup light corn syrup
1/4 tsp kosher salt
1 TB. pure vanilla extract
Combine gelatin and 1/2 cup of cold water in the bowl of an electric mixer fitted with the whisk attacment and allow to sit while you make the syrup.
Meanwhile, combine the sugar, corn syrup, salt and 1/2 cup water in a small saucepan and cook ove med. heat until the sugar dissolves. Raise the heat to high and cook until the syrup reaches 240 degrees on a candy thermometer. Remove from heat.
With the mixer on low speed, slowly pour the sugar syrup into the dissolved gelatin. Put the mixer on high speed and whip until the mixture is very thick..about 15 min. Add the vanilla and mix thoroughly.
With a sieve, generously dust and 8 x 12 inch nonmetal baking dish with confectioners sugar. Pour the marshmallow mix into the pan, smooth the top and dust with more confectioners sugar. Allow to stand uncovered overnight until it dries out.
Turn the marshmallows onto a board and cut them in squares...( I had a hard time getting them out of the pan so I just cut them with a knife directly in the pan.) Dust with more sugar...So good!