A few hours in the water bath and a quick fry in the pan leads to the best technique for medium rare foods like pork and steak.  The sauce is the blend of sweet and tart to pair with the pork.

For the pork:
1 pork tenderloin
salt
pepper

Set sous vide water bath to 130F.  Salt and pepper the tenderloin and seal in a bag.  Cook in the water bath for 1 to 4 hours.

For the sauce:
1 onion, thinly sliced
3/4 c port
3/4 c dried tart cherries
2T marmalade
3T butter

Remove pork from water bath and discard plastic bag.  Dry gently with paper towels.  Heat a small amount of vegetable oil in a large frying pan over high heat.  Sear the exterior of the tenderloin on all sides, about 2 minutes.  Remove the tenderloin from the heat, lower the heat to medium and saute the onions until softened, 5 to 7 minutes.  Add port and cherries to the pan and continue to cook 4 to 6 minutes longer until syrupy.  Remove from heat and whisk in marmalade and butter.  Slice pork loin and serve with sauce.