Sprinkle deer tenderloin with salt, pepper, and chopped rosemary. Let meat sit at room temperature ~ 15 minutes.
Bring a medium size pan to medium high heat. Cast iron works well because it can go from stovetop to oven.
Add olive oil and butter. When melted and hot, sear tenderloin on all sides (usually there are 3 sides) ~ 2 minutes or until browned. The first seared side generally takes ~ 1 minute more.
Transfer to oven and cook an additional 7-10 minutes or until internal temperature of deer reaches 145F. Remember - the oven time will need to increase if you are working with a larger tenderloin(s).
Let meat rest ~ 15 minutes and thinly slice. Add salt to taste. Happy Eating! Beckie
Notes
The meat should naturally come easily off the pan when it's done. If you're not sure if it's ready it's ok to take a quick peak under an edge, but generally you don't want to disturb the meat while it's searing. If it's not letting go of the pan than it is generally not ready.
Butter burns easy. If you find the butter burning before the meat is browning then add a little vegetable or olive oil to bring down the smoking/burning point.
Don't like or have rosemary? Skip it. Just butter, salt, and pepper is perfect.
Please note: I have edited this recipe Aug 2021 to add a little olive oil to add with the butter. It tempers the butter so the meat doesn't burn if you have the pan really hot.