In the bowl of an electric stand mixer, pour 1/2 cup water. Sprinkle the gelatin over the top of the the water, do not stir, and allow that to sit while you prepare the sugar mixture.

In a large pot, combine the remaining 1/2 cup water, sugar, corn syrup, and salt. Bring to a low boil as you stir so the mixture becomes well combined and the sugar dissolves into the mix. Use a candy thermometer to monitor the temperature of the mixture. Once the sugar mixture reaches 240°F (soft ball stage), remove from heat.

With the electric stand mixture running on low, carefully pour the hot sugar mixture into the bowl. Be very careful not to spill any on your skin. Once you’ve added all the sugar mixture to the bowl, turn the mixing speed up to medium/high (around “6” if using a KitchenAid mixer).

Allow to mix for 4-5 minutes until the mixture begins to look white and fluffy. Add the extract to the bowl while it’s still running. Continue to mix for another 2-3 minutes. You’re looking for a total mix time of 7-9 minutes, so the mixture will be very fluffy and thick, like marshmallow creme. during the last 30 seconds, add the chopped rosemary. If you want to color the mixture, add food coloring at this time as well.

Meanwhile, combine the powdered sugar and corn starch. Spray a square 8×8 inch pan with nonstick cooking spray and lightly sprinkle the powdered sugar/corn starch mix over it, taking care to coat the corners well.

Once your marshmallow creme is ready, pour into the pan. Sprinkle the top with the remaining powdered sugar mixture, cover and allow to set for 6-8 hours (overnight).

Then, on a surface dusted with powdered sugar, carefully pull the corners of the marshmallow block out of the pan. Flip the entire mix out onto the prepared surface. Use a knife or pizza cutter to cut into small squares. Toss in powdered sugar before storing.