Place a frying pan onto a medium-high heat and toast the bottom halves of the brioche buns, set aside. Season the venison mince with salt and pepper and shape into 2 thin burger patties, put a splash of oil in the pan and chuck the patties in, they'll cook quickly so be careful, and flip after 1 or 2 minutes when nicely browned.
Then working quickly, put a spoonful of onion relish onto each patty, 3 or 4 slices of beetroot and crumble the blue cheese over the top. Quickly cover with a pan lid and allow to steam and melt the cheese for 2 minutes, remove from the pan and place a patty onto each of the brioche bases. Using the tops of the buns mop up all the juicy goodness left in the pan and serve.