Melt 3 Tbls butter in a large skillet on medium heat.
Increase heat to med-high and brown the beef and reserve.

In the same pan, add 2 Tbls butter, reduce heat to medium, and add the shallots and sauté for 1 to 2 minutes and reserve.

In the same pan, add 2 Tbls butter, increase heat to med-high, and add the mushrooms and sauté for about 4 minutes.
While cooking the mushrooms, add nutmeg and tarragon.

Reduce heat to low add sour cream to the mushrooms.
If you prefer a thinner sauce, you can add a Tbls of stock.
Mix the source cream thoroughly. Do not let it come to a simmmer.

Add the beef and shallots back to the mushrooms, and mix thoroughly.
Salt & pepper to taste.