2) Slice the venison tenderloin into .8-cm slices.
3) In a shallow dish, mix together the flour, mustard powder, cayenne, salt and pepper. In a separate shallow dish, mix together the buttermilk and whole-grain mustard. Dredge the medallions in the buttermilk mixture for a minute. Then coat with the flour mixture.
4) In a cast iron skillet over medium-high heat, heat the oil. Fry the venison until golden brown on both sides. Place on a paper towel lined plate to drain. Serve with feta sauce.