I have done this both in the microwave and on the stove. I prefer the stove because I have more control over everything. If you choose to do it on the stove just bring it to a boil and boil until the whole thing turns clear. Chucks will start to turn little by little and then all of the sudden, you have piping gel.
¼ cup white corn syrup
¼ cup cold water
1 tbsp cornstarch
½ teaspoon white vanilla
1. In a microwave bowl, mix cold water and cornstarch together.
2. Add corn syrup and white vanilla. Stir until combined.
3. Microwave on high for 1 min 30 seconds – 2 minutes until mixture boils and turns clear.
4. Remove from microwave and let cool. Whisk occasionally while cooking.
5. Add food dye (gel) to make desired color.