The secret to Pop Rocks is the pockets of carbonation that are released when they touch your tongue. This recipe uses citric acid to get the same effect.
Many thanks to Emily Jacobs of Sage Recipes for helping with the development of this recipe.
Lightly dust the back side of a baking sheet with cornstarch.
In a medium saucepan, combine the sugar, corn syrup, and water. Cook the mixture until it reaches 300 degrees when measured with a candy thermometer. Remove from heat, and add the baking soda, ¼ cup of the citric acid, extract, and food coloring, and stir to combine.
Spread the mixture out onto the baking sheet (carefully so that it does not run over the edges), sprinkle with the teaspoon of citric acid, and allow to cool completely, about 30 minutes. Break the candy into pieces and add to a Ziploc bag. Using a rolling pin, crush the candy into tiny little pieces so that it resembles Pop Rocks. Store in Ziploc bags.