- 3 1/2 envelopes unflavored gelatin
- 1c cold water, divided
- 2c sugar
- 1/2c corn syrup
- generous 1/4tsp salt
- 2 large or 3 medium egg whites
- 1 Tbsp vanilla
- Powdered sugar
- other flavorings or coloring as desired (you can add a few drops of almond, mint, cherry, food coloring, etc.)
- Spray a metal 9 x 13 pan generously with cooking spray. Sift powdered sugar to coat. Set aside.
- In the bowl of a stand mixer or a large metal or glass bowl, sprinkle gelatin over 1/2c of the cold water and let stand to soften.
- In a 3-quart saucepan, cook sugar, corn syrup, remaining cold water, and salt over low heat. Stir with a wooden spoon till sugar is dissolved. Increase temperature to medium and bring mixture to a boil without stirring until a candy thermometer reads 240 degrees (this takes 10-12 minutes).
- Remove pan from heat and pour sugar mixture over gelatin mixture, stirring to dissolve gelatin. With the whisk attachment on the stand mixer or using a hand mixer, beat mixture on high speed until white, thick, and tripled in volume (this takes 5-7 minutes with a stand mixer or about 10-15 with a hand mixer).
- In a separate medium bowl with clean beaters, beat egg whites until they reach the soft peak stage. Beat in the vanilla, flavorings, and any food coloring, if using, until you’ve just reached stiff peaks. Pour into the baking pan and smooth with a spatula (Don’t worry yourself about scraping out every last bit. If you try too hard, you’ll end up with a sticky mess).
- Sift about 1/4-1/3c powdered sugar over the top of the mixture and place uncovered in the refrigerator to set. Refrigerate at least 3 hours or up to 1 day.
- Remove pan from refrigerator and run a knife around the edges of the pan. Invert the pan onto a large cutting board and loosen one corner of the marshmallows with your fingers. The rest should come out easily, but you may need to continue loosening until the entire block has come out.
- Slice into squares or rectangles of desired size (a pizza cutter worked well for me) and toss with more powdered sugar to coat all the sides. Store at room temperature in an airtight container up to 1 week for best results.**
- **I recommend making these at least the day before you want to use them to allow the flavor to develop.