Preheat oven to 220F.

Make sure your bowl and whisk are completely clean and the egg whites don’t have any egg yolk in them. Line two baking sheets with parchment paper.

Wipe the inside of the stand mixer bowl and the whisk with the lemon slice.

In a stand mixer fitted with the whisk attachment, whisk the egg whites and vanilla extract at medium-high speed until the mixture forms soft peaks.

Slowly add the sugar, about 1 Tablespoon at a time, with the mixer running and beat well after each addition until all the sugar is incorporated.

Once all of the sugar has been added, beat until sugar has just dissolved and the mixture is glossy and stiff about 4 minutes. The sugar should be completely dissolved and the mixture should not be gritty if you rub it between your fingers. It should not be dry, avoid overmixing.

Spoon the meringue into a large pastry bag fitted with a large star tip. Pipe 1.5-inch cookies onto the lined baking sheets, leaving 1 inch between each cookie. They will increase in size a little bit as they dry out.

Bake for 60 minutes, then turn off the oven and leave the cookies in the oven (don’t open the door) until they are cool so they dry out completely. The cookies should be crisp on the outside, lift from the baking sheet without sticking. and sound hollow when tapped on the bottom.

As soon as the meringue is cool, transfer the cookies to an airtight container.