Lay out a sheet of parchment on a baking sheet and ready six small piping bags fitted with round tips or sandwich bags.
Mix together the powdered sugar, meringue powder, and salt in the bowl of your stand mixer or a medium-sized mixing bowl.
2 cups (240 grams) powdered sugar, 1½ tablespoons (14 grams)meringue powder, 1 pinch salt
Add three tablespoons of water and the vanilla to the powdered sugar mixture and beat until the mixture is glossy and you get very firm or stiff peaks so that when you turn the beater upside down, the mixture remains upright or only the tip bends over. If it seems too thick, add a bit more water, about a teaspoon or so at a time.
3 to 5 tablespoons room temperature water, 1 teaspoon vanilla extract
For rainbow sprinkles, divide the mixture into six small bowls and use food coloring for red, orange, yellow, green, blue, and purple sprinkles. Mix until there are no more traces of white, and cover 5 of the bowls with plastic wrap.
food coloring
Spoon one color sprinkle mixture into a bag and snip a small hole at the end. Pipe thin lines on the parchment paper - the lines can be very close together - then proceed with the next color.
Let the sprinkles dry for at least eight hours, then cut them to desired lengths.
Store unused sprinkles in a air-tight bag or tupperware container.