Preheat oven to 220°C (200°C Fan). Then, grease and line a round 20cm cake tin.
Sift the flour, baking powder, sugar and salt into a large bowl.
Add the margarine and rub in with your fingers until the mixture resembles even breadcrumbs.
Create a well in the mixture and add the egg and milk to the centre.
Mix together until just combined fully. It will look like Voldemort's rotting flesh but that's okay.
Spread mixture into the prepared cake tin. Bake for 15-20 minutes until golden brown.
Remove from the oven when cooked through and the top has a light golden brown colour. Leave to cool.
Once cool, carefully cut the cake horizontally in half so you create two layers.
On the bottom piece, spread an even layer of strawberry jam.
Using a freestanding mixer or electric whisk, mix together the double cream and icing sugar on a medium/high speed until the cream becomes fluffy.
Cut the tops off of the strawberries (setting aside some whole ones for decoration) and then cut them half. Arrange on top of the strawberry jam layer.
Pile the whipped cream on top of the strawberry layer (setting some aside for decoration) and spread into a level layer with a knife.
Place the top layer of the cake on top of the whipped cream.
Put the remaining whipped cream into a piping bag and pipe tall rosettes on the top of the cake. Push a small strawberry into each rosette.
Sprinkle over icing sugar for final touch.