Pre-heat the oven to 180 degrees (335 Fahrenheit).

Cut out four small circles of greaseproof paper and place them at the bottom of four cake tin holes. Grease tins with a little butter if not non-stick.

Beat together the margarine and the sugar until lightened in color. Add the egg and a small splash of vanilla extract. Beat in the baking powder and flour until smooth.

Divide the batter between the tins, filling just under 3/4 full. Bake for 12 minutes or until golden and a toothpick comes out clean.

Once cool enough, turn the cakes out onto a wire rack to cool completely.

While the sponges cool, puree the strawberries with lemon juice. Press through a fine sieve to discard seeds.

Beat together the butter and icing sugar until smooth, gradually adding the strawberry puree until combined.

Finely chop the pistachios. Slice each sponge horizontally to make mini sandwich cakes. Fill with strawberry buttercream and refrigerate for 10 minutes.

Spread buttercream around the edges and over the top of each sponge. Roll the sides in chopped pistachios.

Refrigerate for another 10 minutes to set, then allow to come to room temperature before storing.