1. Clean venison tenderloin of all fat and silver skin. Then season with salt and freshly ground black pepper, to taste. Set aside to allow meat to come to room temperature. At this point, you may want to start getting your grill pan or heavy frying pan ready.
2. Chop mushrooms to get one cup. You want the mushroom pieces to be fairly small since it will be part of the sauce.
3. Do the same with 1/2 cup of onion.
4. In a medium sauce pan or skillet, melt 2 tbs. of butter over medium heat. Saute onion until it’s just about to brown. Stir frequently. Then add mushrooms and continue to saute for another 5 minutes, or until mushrooms are cooked and liquids are evaporated. Stir in a pinch of salt. Stir frequently.
5. So you don’t burn your house down, turn off the burner for a moment. Carefully pour 1/2 cup of whisky into the pan. Then turn burner back on to medium heat and simmer until alcohol evaporates, like in the photo. This should only take about a minute. Once whisky evaporates, turn the burner up to medium-high heat and pour in 1/2 cup of beef stock. Allow mixture to reduce by half.
6. At this point, you can choose to scoop out half of the mushroom pieces. We did that for aesthetic purposes. Then we sprinkled those scooped out pieces over the finished dish to make it pretty.
7. Then reduce heat to low. Whisk in 1/4 to 1/2 cup of sour cream and 1/2 tsp. of prepared horseradish, or to taste. You may want to go stronger on the horseradish. Whisk in a few tablespoons of milk to loosen up the sauce. Add salt and pepper, to taste. Stir in chopped chives.
Remember to check on your meat on the grill. Ideally, you want the sauce and the tenderloin to come out at the same time. DO NOT OVERCOOK venison. Medium to medium-rare is bueno.
8. Allow tenderloin to rest 5 minutes after taking off the grill pan. Then slice tenderloin into medallions.