Gather your ingredients!
Mix 3 tablespoons of gelatin with 1/3 cup of cold water in a small bowl. Set it aside to rest for 10 minutes.
Mix 3 cups of sugar with 1 1/2 cups of water in a pot over low heat. Stir to dissolve the sugar.
Add the gelatin to the pot and mix until it dissolves. Without stirring, bring the pot to a gentle boil for 15 minutes. Remove it from heat and let it cool.
Pour the mixture into a bowl and add 1 1/2 teaspoons of vanilla extract. Beat the mixture for about 5 minutes until it thickens and turns white.
Pour the thickened mixture into a greased 9x13 inch pan and let it set overnight.
Once the marshmallows have set, use a knife dipped in cornstarch to cut them into squares. You can even use a cookie cutter to create fun marshmallow shapes! Dust them with cornstarch and confectioner's sugar to finish them off. Yum.