Beat the custard powder, icing sugar, butter, vanilla and 1 tbsp milk together in a stand mixer until smooth and creamy, or do this in a large bowl using an electric whisk. Add a little more milk to loosen, if needed. Transfer the icing to a piping bag fitted with a large star-shaped nozzle and set aside.

Choose three of the best-looking strawberries, then halve and set aside for decorating later (or you can use six whole strawberries). Halve, hull and chop the rest of the berries, then mix with the cordial.

Cut the madeira sponge into roughly 2cm cubes. Arrange a layer of sponge pieces in the bottom of each jam jar, then top with a generous spoonful of the chopped strawberries, including any juice. Pipe a swirl of the custard icing on top, then repeat the layers again, finishing each jar with a strawberry half. Will keep chilled for up to a day.