Start by combining the 3 pkgs. of unflavored gelatin in 1/2 C. cold water in your mixer bowl with the whisk attachment. Let it sit while you make the syrup.
Combine the sugar, corn syrup, salt and 1/2 C. water in a small saucepan. Cook over medium heat until the sugar dissolves. Raise the heat to high and cook the syrup until it reaches 240 degrees on a candy thermometer. Then remove from the heat.
TIP:It makes it easier to handle by pouring the syrup to a container with a pouring spout, such as, a liquid glass or silicone measuring cup.
Turn the mixer on low and slowly begin pouring the syrup into the dissolved gelatin. Then turn the mixer to high and whip until the mixture is very thick and glossy, about 15 minutes. Add the vanilla and mix in thoroughly.
Dust a 9 x 12 nonmetal dish with confectioner's sugar.
TIP: It's easier to line the pan with parchment paper, dust with confectioner's sugar, so that you can then lift out and then cut after they have dried.
Using a rubber scraper, add marshmallow mixture to the dish.
Level off the marshmallow mixture and cover with more confectioner's sugar.
Allow to stand uncovered overnight until it dries out.
Cut marshmallows in squares or with a cookie cutter dusted with confectioner's sugar. Then coat each side with more confectioner's sugar sealing all of the edges.
TIP: If using a cookie cutter, cut as many as possible from the recipe. I save the extra bits to cut into small miniature marshmallow bits to add to hot cocoa or other recipes.A pizza cutter is great for cutting marshmallows into squares. Package in clear bags for gift giving or store in an airtight container.