Set the oven to 300°F (150°C). Prepare two large baking sheets by lining them with parchment paper or silicone baking mats. If using parchment, apply a small dab of meringue batter under each corner to keep the paper from shifting during preparation.

In a stand mixer fitted with a whisk attachment, combine the egg whites and a pinch of salt. Begin mixing on low speed, gradually increasing to medium. Beat until the mixture becomes foamy and soft peaks start to form, about 2 to 3 minutes. The bubbles should be small and uniform.

Increase the mixer speed to medium-high. Slowly add the sugar, about 1 to 2 teaspoons at a time, allowing each addition to fully dissolve before adding more. Once all the sugar is incorporated, add the white vinegar. Continue beating on high speed until the egg whites form stiff, glossy peaks—approximately 4 to 5 minutes.

Using a rubber spatula, gently fold in the crushed peppermint candies and, if desired, the mini chocolate chips. Take care to maintain the airiness of the meringue while evenly distributing the mix-ins.

Transfer the meringue mixture into a pastry piping bag fitted with a large round or star tip, or use a resealable plastic bag with one corner snipped off. Pipe 1½-inch mounds onto the prepared baking sheets, spacing each about 1 inch apart. Alternatively, drop spoonfuls of the mixture onto the sheets for a more rustic appearance.

Place both trays in the preheated oven and bake for 1 minute only, then immediately turn the oven off. Do not open the oven door. Leave the meringues in the closed oven for at least 3 hours, or overnight, allowing them to dry slowly in the residual heat.

Once the meringues are fully set, remove them from the oven. They should be crisp on the outside and light inside. Store in an airtight container at room temperature for up to 1 week.