Preheat oven to 275F. Line two baking sheets with parchment paper or silpats (see note) and set aside.
In the bowl of a stand mixer, beat egg whites and cream of tartar on medium speed with the whisk attachment until frothy. Increase the speed to high and beat to stiff peaks.
With the mixer still running, gradually add the sugar and salt. Stop the mixer to scrape down the sides of the bowl, then beat on high for five minutes. Mixture will be white, stiff, and glossy.
Add vanilla bean paste, blueberry powder, and food coloring (if using) and mix to combine. Pipe meringue onto the prepared sheets (each of my meringues were about 1 ½" across).
Bake meringues about 40 minutes, turning them around half way through baking. Meringues will be crisp on the outside and slightly chewy in the center. Allow meringues to cool completely on the pan before trying to move them.
Line baking sheets with waxed paper or parchment. Once meringues are cooled, dip the bottoms of each in chocolate (then in sprinkles, if desired!) and place on prepared baking sheets. Allow the chocolate to set completely before serving.Enjoy!
Notes
Note on vanilla bean paste: You know me, there's vanilla bean paste in everything! I love the flavor and it's cheaper than using whole vanilla beans. You can substitute with half a vanilla bean or with ½ teaspoon of vanilla extract if you like. If you're looking to purchase vanilla bean paste and can't find it in your local grocery store (I never can), you can find it online [here].Note on blueberry powder: These gems get their blueberry flavor and color from freeze-dried blueberries (like these [here]). Just grind them into a powder in a food processor and you're good to go. Note that this recipe is very sensitive to humidity, both in getting the powder to grind up nicely and in baking the meringues themselves. If it's a humid day, I wouldn't set about to make these!Note on silpats: I baked my meringues on silpats because they're reusable, nothing sticks to them, and the bottoms of the meringues brown more slowly. If you'd like to get some silpats for yourself, you can find them [here].