These tiny, lemon-flavored meringues must be cooked slowly so their outsides are powdery and crisp, while the insides are chewy and yielding. Serve with sorbet.
Preheat oven to 250 degrees F. Cover two baking sheets with parchment paper or foil.
Beat egg whites with salt until soft peaks form. Add sugar very slowly, beating well between additions, until egg whites are stiff but not dry. Fold in lemon zest and vanilla.
Drop by teaspoonfuls onto the baking sheets or pipe small kisses with a pastry bag, fitted with a 1/2-inch star tip. Bake until dry but not brown, 40 to 45 minutes. Cool 2 to 3 minutes before removing from the baking sheets.
Make Ahead Tip: Store in an airtight container for up to 2 weeks.
Tip: To bring an egg to room temperature, either set it out on the counter for 15 minutes or submerge it (in the shell) in a bowl of lukewarm (not hot) water for 5 minutes.