1. In a saucepan, combine liqueur, honey, berries, sugar and salt and simmer on medium-high heat until reduced by half. Remove from heat and all to cool completely.
2. In a mixing bowl, combine reduction, Plugrá Butter and tarragon until well combined.
3. Remove butter from bowl and spoon onto parchment paper. Roll into a log, using edge of baking sheet to form a tight log. Chill for 2 hours before serving.