Preheat the oven to 200C/Gas 6; put the walnuts in a bowl with the sugar, add ½ tablespoon of water and toss to coat; scatter them in a small oiled roasting tin and bake for 10-12 minutes until golden; remove from the oven and allow them to cool
Toss the potato wedges in 1 tablespoon of the sunflower oil and spread out on a large baking sheet; season lightly, mix and bake for 30-40 minutes until tender and beginning to brown, allow to cool slightly, then put into a bowl
Whisk together the vinegar, remaining sunflower oil, the walnut oil and the remaining sunflower oil; season to taste; reserve a tablespoon of the dressing and pour the rest over the warm sweet potatoes; mix well and allow to cool completely
Cut the apples into match sticks and toss in the reserved dressing; roughly chop the cooled walnuts
Arrange the potatoes on a large platter, scatter over the apples and walnuts and crumble the Stilton on top just before serving
6 servings