Preheat oven to 180 °C. Grease and line a 22 cm springform tin.
Beat the butter and sugar until creamy. Add the egg yolks, vanilla and lemon zest and beat until combined. Gradually add the milk, beating well as it incorporates.
Stir the flour into the butter mixture until a thick batter forms. Scrape the batter into the prepared springform tin, smooth the top and bake for 20 minutes.
Remove the cake from the oven and spread the top evenly with the jam. Put it back into the oven for 10 minutes while you make the meringue topping.
Whisk the egg whites and lemon juice until soft peaks form. Add the caster sugar 1 tablespoon at a time, whisking well after each addition. Whisk for about 5 minutes once the last of the sugar has been used.
Take half a cup of the meringue and combine it with the 4 tablespoons of jam and food colouring. Stir well. Gently fold the remaining meringue into the coloured mixture, stirring 3 or 4 times. Don’t over mix it as you want to retain the streaks through the meringue.
When the cake comes out of the oven, reduce the heat to 150°C.
Pipe the meringue onto the hot cake, put it back into the oven for 10 minutes, then turn off the heat. Leave the cake in the oven until it has cooled completely and the meringue has set and is dry on the surface.
Dust generously with icing sugar and serve with double cream. Personally I think it’s best eaten at room temperature, or slightly warm.