Set sous vide machine to 55C/131F.
Season beef tenderloin lightly with salt and pepper. Place meat in sous vide bag and remove the air through a vacuum sealer or the displacement method. Drop the bag in the bath for two hours.
Remove bag from bath. Take tenderloin out of the bag, pat dry with paper towels and season with salt and pepper to taste.
Heat up large skillet on high and add butter. Sear tenderloin for 1 to 2 minutes on each side. Remove from pan, and place on a plate to rest for 5 minutes. Once rested, serve and enjoy! Alternatively sear the beef on a grill or using a searing torch.
Place fresh blackberries and blackberry jelly into a small sauce pan over low heat. Sprinkle white sugar on top, do not stir. Bring to a simmer until sauce begins to form, approximately 10 minutes.
Turn heat to medium and add balsamic vinegar, beef broth, red wine, and garlic. Cook for 10 minutes until sauce thickens. Remove from heat and strain into a mesh sieve into a container. Pour sauce in container back in sauce pan on medium heat and simmer until thickened to your preference. Turn off heat and add ½ tablespoon of butter. Gently fold in to sauce until well combined.