Heat the oven to 180C/160C fan/gas 4. Lightly grease a medium baking dish with 1 tsp of the spread. Put the remaining spread, caster sugar, lemon zest, egg, flour, baking powder and yogurt in a mixing bowl. Whisk together for 2 mins until pale and fluffy. Stir in the apple sauce – this might make the mixture look curdled, but don’t worry. Gently fold in the berries, then pour the batter into the prepared dish and level the surface. Bake for 25-30 mins until the sponge is golden brown and firm in the centre.