In a bowl, stir together 1/2 cup of lukewarm water and 3 packages of unflavored gelatin. Allow this to stand while you prepare the syrup. This step is crucial as it hydrates the gelatin, ensuring it dissolves properly later.
In a medium saucepan, combine 1 1/2 cups of granulated sugar, 1 cup of light corn syrup, pinch of kosher salt, and the remaining 1/2 cup of lukewarm water. Heat the mixture over medium-high heat, stirring until the sugar completely dissolves.
As the mixture cooks, keep an eye on the temperature. You need to bring it to the softball stage, which is around 240º F. Use a candy thermometer for accuracy. Once it reaches this point, carefully remove it from the heat.
Now, attach the whisk to your electric mixer. With the mixer on low speed, gradually pour the syrup mixture into the swollen gelatin while it’s whisking. This method prevents the gelatin from clumping and ensures a smooth consistency.
After pouring in the syrup, stop the mixer and make sure all the gelatin is loosened from the bowl’s bottom. It’s important for the mixture to be thoroughly combined.
Increase the mixer speed to high and whip the mixture for about 15 minutes. You’ll notice it becoming light and fluffy. The volume will increase significantly, creating that desired marshmallow texture.
While the marshmallow mixture is whipping, prepare your dish. Lightly coat an 8 x 12 glass or non-metallic dish with shortening. Dust with confectioner’s sugar to ensure it’s well coated and prevents sticking.
Once the marshmallow mixture is whipped to perfection, add 2 teaspoons of vanilla extract and mix until well incorporated. This step adds delightful flavor to your marshmallows.
Spread the marshmallow mixture evenly into the prepared dish using a greased rubber scraper. Make sure to smooth the top for even drying.
Dust the top lightly with more confectioner’s sugar and leave it uncovered overnight to dry completely. This drying time is crucial for achieving the right texture.
Once dried, carefully pour the marshmallow out onto parchment paper. Using a sharp knife, cut it into large pieces, dusting the cut edges with additional confectioner’s sugar to prevent them from sticking together.
Store your marshmallows in an airtight container for up to three weeks. Enjoy them in various desserts or on their own!