Preheat the oven to 180C/160C Fan/Gas 4. Sit the venison on a plate, cover with cling film and allow to come to room temperature.
Put the shredded cabbage in a bowl. Mix the mustard, vinegar, sugar and half a teaspoon of the salt together, pour over the cabbage and stir to coat. Cover and set aside.
Put the pumpkin in a roasting dish and add the cumin seeds and curry leaves. Drizzle over one teaspoon of the sesame oil and season with the remaining salt. Toss together and bake for 10 minutes.
Meanwhile, place a medium saucepan over a medium heat. Add the sunflower oil, onion and star anise and cook until the onion begins to caramelise, stirring often. Add the garlic, ginger and chilli and cook for another 2 minutes, stirring. Add the fish sauce and cook for 30 seconds, then add the lemongrass, lime leaves and coconut milk and bring to the boil. Cook over a medium heat for 4 minutes.
Remove the pumpkin from the oven and pour the curry sauce over it. Return to the oven and continue cooking until the pumpkin is cooked and beginning to colour. Turn the oven off and keep the pumpkin warm in the oven.
Meanwhile, to cook the venison, place a heavy-based saucepan over a medium–high heat and wait until it gives off a blue haze. Brush the steaks with the remaining sesame oil and lightly season with salt and pepper on both sides. Place the steaks in the pan and cook for 3 minutes. Turn over and cook to your liking. (If you like it medium–rare, they’ll need just another 2 minutes.) Remove the steaks and rest them on a warm plate, covered with foil, for 5–8 minutes.
To serve, spoon the pumpkin onto four warmed plates and lay the cabbage across it. Slice the venison into 1cm/ ½in slices and lay on top, then spoon over the sauce.