In a small saucepan, simmer the reserved liquid from the can of Oregon Blackberries with balsamic vinegar, salt and pepper on medium low until reduced and slightly thickened (about 10-20 minutes). Stir frequently.
Remove from heat and toss in blackberries.
Spread soft butter on each half of the sliced biscuits.
Add a piece of chicken to each bottom biscuit.
Spoon blackberries and liquid onto the chicken and complete the sandwich with the biscuit top.
If picnicking, wrap each sandwich in a piece of parchment paper and pack side by side in a hard container, in a single layer, so the sandwiches aren’t crushed. Serve with additional blackberries and sauce on the side.