Crush halved strawberries in a large saucepan using a potato masher.
Stir in jam sugar over gentle heat until completely dissolved.
Bring the mixture to a vigorous rolling boil that cannot be stirred down.
Boil for exactly four minutes, then remove from heat to cool.
Preheat your oven to 190°C and grease the mini sandwich tins with butter.
Cream butter and sugar until light, then gradually mix in beaten eggs and vanilla.
Sift in the flour and fold gently until the batter is smooth.
Distribute the batter into the tin cups and level each with a spoon.
Bake for 15 minutes until golden-brown and springy to the touch.
Cool in the tin for two minutes before transferring to a wire rack.
Whip double cream to soft peaks and transfer to a piping bag.
Slice each cooled cake in half horizontally using a bread knife.
Pipe cream dots onto the bases, top with jam, replace lids, and dust with icing sugar.