Combine the vinegar and peppercorns in a small saucepan over high heat and cook, stirring occasionally, until reduced to 1/4 cup, 8 to 10 minutes. Remove the peppercorns, whisk in the honey and rosemary and let cool to room temperature.
Combine the balsamic mixture with the butter and 1 teaspoon salt in a food processor or with a mixer until smooth. Scrape into a bowl and refrigerate 30 minutes to set slightly.
Photographs by Steve Giralt
Recipe courtesy Bobby Flay for Food Network Magazine