Mary Berry Apple Crumble With Walnuts And Oats

Name: Mary Berry Apple Crumble With Walnuts And Oats
Prep time: 10 min
Cook time: 40 min
Total time: 50 min
Cuisine: British
Ingredients: 5 oz (1.5kg) apples, like Bramley or Granny Smith (to get the right acidity and texture.); ½ lemon (juice only); ½ cup (100g) light muscovado sugar; 6 tbsp water; 6½ tbsp (50g) plain flour; ⅓ cup (50g) porridge oats; ¾ cup (150g) light muscovado sugar; 5½ oz (150g) walnuts (roughly chopped); ⅓ cup (50g) sunflower seeds; 3½ oz (100g) unsalted butter (softened)