For the horseradish sauce:

1 cup sour cream
1/4 cup grated fresh horseradish
1 tablespoon Dijon mustard
1 teaspoon White wine vinegar
1/2 teaspoon kosher salt
1/4 teaspoon freshly ground black pepper

Place all of the ingredients into a mixing bowl and whisk until the mixture is smooth and creamy. Place in the refrigerator for at least 4 hours or overnight to allow flavors to infuse together. Sauce can be stored in the refrigerator in an airtight container for 3 to 4 weeks.

For the sirloin strips:

2 lb beef sirloin steaks, at least 1″ thick
salt, to taste
1 teaspoon fresh cracked black pepper
3 tablespoon butter
1 tablespoon olive oil, or any oil w/ high smoke point

Directions

Bring sirloin steak out of the refrigerator and allow it to sit at room temperature for even cooking. Salt and pepper both sides of each steak. Note: I usually use salt after the steak is cooked to maintain juiciness because salt immediately draws moisture out. Heat skillet on high (I use cast iron), Drizzle  oil on pan for a thin coat. Add butter and allow to melt. For medium rare, sear steaks 4 minutes on each side. Turn off heat.Remove steaks from pan and let rest 5 minutes. Then slice thinly against the grain with a sharp knife. Toss sirloin steak strips back into pan with buttered drippings. Stir to coat evenly. Serve immediately over a bed of arugala or salad of your choice and drizzle with horseradish sauce. Bon Appetit!