1. Reduce wine, shallots, pepper, tarragon, and chervil in a flared saucepan over moderate heat to 1/4 cup, about 15-18 minutes. Strain and discard solids. Return wine reduction to the saucepan and reduce by half. Remove from heat and allow to cool to room temperature.
2. Whip Plugrá Butter until smooth and light.
3. Drizzle in wine reduction and whip to combine.
4. Fold in peppercorns and tarragon until well combined.
5. Shape into a log using parchment or wax paper. Refrigerate until firm (about 2 hours), slice into thin rounds as needed or transfer to plastic wrap to store.