Preheat the oven to 190C/375F/Gas 5. Line two Swiss roll tins with greaseproof paper.
For the jam, place the strawberries and sugar in a heavy-based saucepan, bring to a boil and cook for 10 minutes. Transfer to a bowl and set aside to cool.
For the sponge, beat all of the ingredients in a bowl until light and fluffy. Spread the mixture out into a Swiss roll tin, flatten with a palette knife and bake in the oven for 18-20 minutes or until golden-brown and cooked through.
Carefully turn the sponge cake out onto a wire rack, peel off the paper and set aside to cool.
For the buttercream, sift the icing sugar into a bowl. Add the butter and milk and beat until smooth. Spoon the buttercream into a piping bag fitted with a small star nozzle.
Cut 24 x 5cm/2in circles from the sponges, then cut each circle into two sandwich halves. Spread twelve halves with the strawberry jam and pipe on a little buttercream. Sandwich together with the remaining sponge circles. Dust icing sugar over the top of each sandwich.