Makes about 30
5 large egg whites, room temperature
¼ tsp. cream of tartar
¼ tsp. Diamond Crystal or Morton kosher salt
¾ cup (150 g) granulated sugar
¾ cup (83 g) powdered sugar
1 tsp. vanilla bean paste or vanilla extract
A pastry bag and an Ateco #848 or other large star tip
Place racks in upper and lower thirds of oven; preheat to 225°. Place 5 large egg whites, room temperature, in the bowl of a stand mixer fitted with the whisk attachment. Sprinkle ¼ tsp. cream of tartar and ¼ tsp. Diamond Crystal or Morton kosher salt over and let sit 5 minutes.
Meanwhile, sift ¾ cup (150 g) granulated sugar and ¾ cup (83 g) powdered sugar into a medium bowl and whisk to combine.
Beat egg white mixture on medium speed until foamy, 30–60 seconds. With motor running, add sugar mixture 1 Tbsp. at a time, incorporating completely before adding more and scraping down sides of bowl as needed between additions, 6–8 minutes total. Increase speed to high and beat meringue until glossy and stiff peaks form, about 2 minutes. Reduce speed to medium, add 1 tsp. vanilla bean paste or vanilla extract, and beat until just incorporated. (Be careful not to overmix or the meringue will deflate and turn foamy.)
Place a pastry bag fitted with a large star tip into a tall glass or vase and fold the top of the bag over the rim of the glass to hold it in place. Fill bag with meringue, then bring sides together and twist to close. Dab a little meringue in each corner of a baking sheet and line with parchment paper; lightly press meringue dabs to adhere parchment to baking sheet. Holding pastry bag vertically about 1″ above baking sheet and working in an upward motion and twisting at the top to create a swirled shape, pipe meringue to make a 2″-wide star. Repeat to fill baking sheet, spacing meringues about 1″ apart. Repeat process with another baking sheet.
Bake meringues until crisp on the outside and shiny (but not sticky or tacky), 2 hours to 2 hours and 45 minutes. (To check if they are ready, lift a meringue off the baking sheet: it should be light, lift off the baking sheet cleanly, and sound hollow when tapped on the bottom. If meringues are not done after 2 hours, keep baking, checking every 20 minutes.
Turn oven off and leave door slightly ajar (prop open with a wooden spoon if needed). Let meringues cool in oven at least 1 hour and up to 12 hours.
Do ahead: Meringues can be baked 10 days ahead. Store airtight at room temperature. If meringues soften, re-crisp in a 225° oven 10–15 minutes.