Marinating back strap!?
Please don't ruin it like that. This is the second best cut of meat on the deer and it needs no marinating. It has it's own good flavor and is already tender.
We're going to dry brine and reverse sear it, searing at the end, and only salt and pepper seasoning to let the meat speak for itself.
Remove all silver skin(this is where a lot of 'game' taste comes from)
Cut into 8" or so hunks. The bigger the better as we have more meat that's properly cooked...don't do steaks IMO, WAY too easy to overcook.
Dry Brine: Salt the meat about 8 hours before serving with Kosher salt replace in the fridge.
Fresh cracked pepper on the meat just before putting in the oven.
Place in the oven at 250º and cook until the internal temp of about 125ºF. It will carry over to a perfect medium rare.
Once you're getting close to internal temps, get a cast iron pan on and slowly bring it up to very hot. Move the strap to the hot pan and sear on all sides. You can sear it on the grill if you want that flavor, but get it as hot as you can and only sear for short period of time. We're trying to avoi overcooking the outer layer of meat. You want to go from seared outside directly to medium rare inside.
Slice against the grain and enjoy.