Prepare an 9×13 inch pan with a light coat of cooking spray and sprinkle powdered sugar into the pan. Give it a couple of taps over the sink to coat the pan. Set aside.

Pour the Merlot and 4 tablespoons of powdered sugar into a medium saucepan. Bring it to a simmer stirring constantly until the mixture reduces to just about 1/4 cup. The mixture will thicken a bit. Carefully pour the reduced Merlot into a measuring cup and let it cool completely.

Combine the gelatin and 1/2 cup of cold water in the bowl of a stand mixer fitted with the whisk attachment and allow it to bloom for at least 5 minutes.

Meanwhile, combine the sugar, corn syrup, salt, and 1/2 cup water in a small saucepan and cook over medium heat until the sugar dissolves. Raise the heat to high and cook until the syrup reaches 240°F on a candy thermometer. Remove the mixture from the heat immediately.

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 minutes. Add in the vanilla and mix thoroughly.

Dust lightly with powdered sugar.

Place the marshmallows in a dry area uncovered for at least 8 hours or overnight until the marshmallows dry and set.

Run a wet knife around the edge of the pan and turn the marshmallows out onto a confectioner sugar dusted surface. Cut into squares.