1. Heat the oven to 190C/170C fan/gas 5. Lightly oil and line two 20cm loose-bottomed sandwich tins with baking parchment. In a large mixing bowl, cream together the margarine, sugar and 1½ tsp of the Dr. Oetker Vanilla Bean Paste until pale and fluffy. Add the eggs one at a time, mixing well in between (if the mixture starts to curdle, add 1 tbsp flour). Once all the eggs are fully incorporated, whisk in the milk and sift the flour and Dr. Oetker Baking Powder over the mixture, then gently fold using a spatula.
2. Divide the mixture between the prepared tins and bake for 20-25 mins until the cakes have risen and spring back when pressed. Leave them to cool in the tins for 10 mins before transferring to a wire rack to cool completely.
3. Once cool, place one of the cakes on a serving plate, levelling the top with a serrated knife, if needed. In a bowl, sift the icing sugar over the mascarpone, then gently whisk before stirring in the remaining Dr. Oetker Vanilla Bean Paste. Add the double cream and whip to soft peaks, then smooth over the sponge. Arrange the fresh strawberries on top, and spoon over the jam. Carefully top the cake with the second sponge and sprinkle with a little caster sugar to finish. Enjoy immediately or store in an airtight container and eat within 24 hours.