For the strawberry jam, sterilise 4-5 jam jars by washing in a dishwasher on the hot cycle, or wash in hot soapy water, rinse and dry in a low oven for 45 minutes.
Place the sugar, juice and zest of the lemon and three tablespoons water into a large pan and heat slowly until the sugar is melted.
Add the strawberries and stir gently.
Bring to the boil and cook for 3-4 minutes, or up to 10 minutes if you prefer a thicker jam. The temperature should reach 105C/220F on a sugar thermometer.
Leave to cool slightly, skimming off any froth with a clean spoon.
Spoon the jam into the sterilised jam jars, seal and label.
Preheat the oven to 190C/350F/Gas 5. Grease and flour two 23cm/10in sandwich tins.
For the sponge, combine the butter, sugar and vanilla extract in a bowl or a free-standing mixer and beat until light and fluffy. 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 well-risen, golden brown and springy when pressed.
Turn out onto a wire rack and leave to cool.
For the filling, whip the cream until soft peaks form when the whisk is removed and fold in the chopped strawberries and icing sugar.
For the Italian meringue, place the sugar and 125ml/4½fl oz water into a pan and slowly bring to the boil until the syrup reaches 121C/250F on a sugar thermometer.
Meanwhile, place the egg whites into a clean bowl with a squeeze of lemon juice, and whisk until firm peaks form when the whisk is removed.
As soon as the sugar reaches 121C/250F, remove the pan from the heat.
Immediately resume whisking the egg whites. With the beater at its lowest speed, pour in the sugar syrup, in a steady stream, making sure the syrup is clear of the beaters.
Continue beating for about five minutes, until the meringue is tepid.
To assemble the cake, cut the sponges in half across so that you have four thin layers of sponge.
Place one piece of sponge onto the serving plate and spread some of the strawberry jam then one-third of the strawberry cream on top.
Repeat with the other sponges and remaining jam and cream until the four layers are complete.
Spread the Italian meringue over the gateaux to cover completely.
Rough up the meringue with a fork to create little peaks. Garnish with a sprig of holly.