- 4 large egg whites
- 1 cup sugar
- 3 sticks unsalted butter, softened
- 1/2 teaspoon peppermint extract
- Pinch coarse salt
- 3 to 4 drops green food coloring (optional)
Put egg whites and sugar in the heatproof bowl of an electric mixer set over a pot of simmering water. Whisking constantly, cook until sugar dissolves and mixture is warm to the touch (about 160 degrees). Attach bowl to a mixer fitted with the whisk attachment. Starting on low and gradually increasing speed to high, beat egg whites until stiff and glossy and the bottom of the bowl is cool, about 10 minutes. Reduce speed to medium-low, and add butter, a few tablespoons at a time, until incorporated. Switch to paddle attachment, and add peppermint extract, salt and, if using, food coloring. Beat until air bubbles are gone and mixture is smooth. Store in an airtight container and refrigerate up to 3 days. Bring to room temperature and re-whip with paddle attachment before using.