Note: These sprinkles are tons of fun to decorate with, but I don't recommend adding them into cake or cupcake batter! They tend to sink to the bottom and kind of dissolve as the cake/cupcakes bake.Add 2 cups of powdered sugar (if you notice any clumps in your powdered sugar, be sure to sift it), 3 tablespoons of water, 1 1/2 Tbsp of light corn syrup, 1 Tbsp of vanilla extract (optional), and 1/4 tsp of fine salt into a large bowl. Either whisk or mix together with a hand mixer on a low speed until smooth. Scrape the sides and bottom of the bowl with a rubber spatula. Then add the remaining 1 cup of powdered sugar and mix until combined. The final consistency should be thick but still pipeable. If you want to test the consistency, you can place a Tbsp in a piping bag and try piping a short line. If the mixture seems too thick to pipe, mix in more water, one teaspoon at a time.
If you want to make different-colored sprinkles, divide the mixture evenly between a few small bowls and mix in gel food coloring. One batch makes about 460g. If you want to make the 6 classic rainbow colors (red, orange, yellow, green, blue, purple), use about 75g of the mixture per color. Note: If you use liquid food coloring, it may thin out the mixture a bit. If you notice that, you can add in more powdered sugar, 1 tbsp at a time.
Pour each color into its own small piping bag. When you're ready to pipe the sprinkles, cut a small opening (about 1/16 inch) at the bottom of the bag. If the opening is too large, the sprinkles will be thick and can be difficult to cut. Pipe lines or shapes onto a baking sheet lined with parchment paper and set aside to dry for at least 8 hours or overnight.
Once they're fully dry, cut the sprinkles into small pieces with a sharp knife. If you pipe custom sprinkles, gently lift them with your finger to remove them from the parchment paper. You can also use a flexible bend scraper to help them release.
Gently lift the parchment paper to pour them into an airtight container and store them somewhere dark (like a cupboard or pantry) until you're ready to use them. Moisture will cause them to soften, so if you live somewhere humid, be sure they're stored in a container with a good seal. They can be stored at room temperature for up to a year in an airtight container.