Heat oil and butter in a frying pan. Add medallions and sear over high heat until desired level of doneness is achieved. Salt and pepper. Keep warm.
In the same pan, add 15 ml (1 tbsp.) oil and brown shallots for 1 minute over medium-high heat. Add balsamic vinegar and reduce for about 2 minutes, stirring constantly, until syrupy.
Add maple syrup and reduce for 2 minutes, stirring constantly. Add beef stock and reduce by half. Add cream and horseradish and stir for 1 minute.
Add blueberries and cook for 1 minute. Serve over venison medallions.