A moist apple sponge with crunchy demerera topping.
Line a baking tin roughly 20cm x 25cm with greaseproof paper or baking parchment, (NB it is helpful to leave a bit of extra paper overlapping the edges, so that you can get it out of the tin without tipping it up and losing the demerera toping!). Preheat the oven to 175C (fan) / 350F / Gas Mark 4.
In a food mixer or large bowl, whisk together the margarine and soft brown sugar for 2-3 minutes. Add the soya yoghurt and milk and whisk again, then stir through the cinnamon, lemon zest and oats.
Sieve the flour and baking powder into the mixture. Stir gently until just combined, then fold through the apples and sultanas.
Tip the mixture into your baking tin and smooth out the top. Sprinkle with the demerera sugar, then bake for 60-80 minutes until a skewer comes out completely clean, (NB a slightly larger tin = shallower cake, so it will cook more quickly).