For the jam, heat the sugar, lemon juice and zest and three tablespoons water in a large pan, slowly, until the sugar has melted.
Add the strawberries and stir gently.
Bring the jam up to the boil and cook for 3-4 minutes, or up to 10 minutes if you prefer a thicker jam.
Check the temperature with a sugar thermometer – it should reach 105C/220F.
Remove the jam from the heat and leave to cool slightly. Skim off any froth with a clean spoon, to stop the jam from going cloudy.
Spoon the jam into a sterile jam jar, seal and label.
For the cake, preheat the oven to 190C/375F/Gas 5.
Grease and flour two 20cm/8in sandwich tins.
Combine the butter, sugar and vanilla essence in a bowl or food processor, and mix well to a creamy consistency.
Slowly beat in the eggs one by one.
Fold in the sifted flour then pour the mixture into the prepared tins.
Bake for 20-25 minutes until the sponge is well-risen, golden-brown and springs back when pressed.
Remove the cakes from the oven, turn them out of their tins onto a wire rack and leave to cool.
Spread one cake with strawberry jam, followed by a layer of whipped cream.
Layer on the fresh strawberries then place the other cake on top.
Dust with icing sugar to finish.