For the strawberry purée, place the chopped strawberries, sugar, juice and cornflour into a saucepan and cook over medium heat, stirring frequently for approx. 5 minutes until thick. Chill until needed
Preheat oven to 180°C (160°C fan) and line two 2lb loaf tins with parchment.
Cream butter and sugar until pale and fluffy. Add eggs one at a time, mixing well after each.
Add flour, ground almonds, and baking powder, then mix. Stir in milk to reach a dropping consistency.
Divide the batter into two bowls. Add the cold strawberry purée to one and mix. Pour into tins, smooth the tops and bake for 45–50 minutes until a skewer comes out clean.
Cool completely on a wire rack, then chill for 30 minutes to make trimming easier.
Trim off crusts and cut each sponge into four even strips lengthwise.
Glue strips together with the jam, alternating colours to form the classic chequered pattern.
Chill briefly while preparing the icing.
Roll the icing into a rectangle large enough to wrap the cake. Brush lightly with more jam.
Wrap the sponge in icing, smoothing and sealing the edges.
Trim the ends to reveal the pattern and store in a cool, dry place until serving.