Place all the ingredients for the toffee sauce into a microwave-safe jug or bowl, (a fairly large one as the sauce will bubble up as it cooks), and microwave it on full power for 1 minute 30 seconds. Stir it and return to the microwave for a further 1 minute 30 seconds then set aside to cool.
For the Cake:
Place the dates, bicarbonate of soda and apple juice in a saucepan, bring to the boil then simmer on a low heat for 10 minutes. When the dates are soft, mash with a fork or blitz with a hand blender until fairly smooth.
Preheat the oven to 180C / 350F / Gas Mark 4. Line the base of a 22cm cake tin with baking parchment, then pour a thin layer of toffee sauce over the base. Place the tin in the freezer (or fridge if you don't have space!) until needed.
Beat together the margarine and sugar until light and fluffy, then stir in the soya yoghurt and milk.
Peel and core the apples. Cut two of the apples in half, then slice them finely and arrange the slices over the toffee sauce in the base of the cake tin, overlapping each slice to make a pretty pattern. Cut the remaining two apples into large chunks.
Sieve the flour, baking powder, ground cloves and cinnamon into the mixture and fold in slowly until combined. Roughly chop the walnuts and stir through the mixture along with the apple chunks and mashed dates.
Pour the cake mix into the tin carefully, (keeping the apple pattern in tact as much as possible!), then smooth it flat. Cover a baking tray with foil and put your cake tin on the tray (to catch any sticky toffee drips), and place in the oven. Bake for 50-60 minutes until a knife comes out clean, covering the top of the cake with foil if it looks like it might be getting too brown on top towards the end of cooking time.
Leave to cool in the tin for 2-3 minutes, then turn out onto a cooling rack, and carefully peel off the baking parchment to reveal the apple pattern. When it is completely cool, drizzle over some of the remaining toffee sauce. Serve the rest of the sauce in a jug alongside the cake.