Pierce the venison steaks with a fork all over – this helps tenderise them. Dust the steaks with a good pinch of salt and pepper. Pop them in a dish or on a plate. Mix ½ tbsp Dijon mustard (kep the rest for later) and 1 tsp of the fennel seeds and rub this all over the steaks, on both sides. Set aside.
Peel and coarsely grate the beetroot. Halve, peel and finely chop the red onion. Finely dice the celery. Peel and finely chop the garlic. Finely chop the chives.
Set a large pan over high heat. Add 1 tsp olive oil. Add the remaining fennel seeds, the veg and garlic with a good pinch of salt and pepper. Lower the heat to medium. Stir and fry for 5 mins till softened.
Add the buckwheat. Stir for 1 min to toast a little. Pour in 400ml boiling water. Bring to the boil. Lower heat. Simmer 15 mins, stirring often, till the water had been absorbed.
Swirl the remaining mustard through the buckwheat risotto. Add most of the thyme leaves to the buckwheat and stir them through. Taste. Season to your liking with salt and pepper. Set aside, with the lid on, to keep warm.
Warm a frying or griddle pan over high heat. Rub ½ tsp oil into each steak. Press into the hot pan. Fry for 2-4 mins each side, or for a few mins longer for well-done steaks, or if they're very thick steaks.
Spoon the buckwheat risotto into bowls. Add spoonfuls of the yogurt to each bowl. Thinly slice the steaks. Perch them on top. Sprinkle with the remaining thyme leaves to serve.