To make the lemon sour cream cake, preheat oven to 180°C. Grease a 20cm round cake pan and line the base and side with baking paper.
Use an electric mixer to beat the butter, sugar and lemon rind in a bowl until pale and creamy. Add the eggs, 1 at a time, beating well after each addition. Add the combined flour, and the sour cream and lemon juice, in batches, stirring well after each addition. Spoon into the prepared pan and smooth the surface. Bake for 45 mins or until a skewer inserted in the centre comes out clean. Turn onto a wire rack to cool completely.
To make the lemon curd, combine the lemon rind, lemon juice, sugar, butter and egg in a saucepan over low heat. Cook, stirring constantly, for 5 mins or until the mixture coats the back of a spoon. Strain through a fine sieve into a clean bowl. Cover with plastic wrap. Place in the fridge to chill.
To make the meringues, preheat oven to 100°C. Line a baking tray with baking paper. Use an electric mixer to whisk egg whites in a clean, dry bowl until soft peaks form. Gradually add the sugar, 1 tbs at a time, whisking well after each addition. Continue whisking until sugar is completely dissolved. Place in a piping bag fitted with a 1cm fluted nozzle. Pipe meringues onto the lined tray. Bake for 1 hour or until dry to the touch. Turn the oven off. Leave meringues in the oven, with the door ajar, for 1 hour to cool completely.
Use an electric mixer to whisk the mascarpone, cream and half the lemon curd in a bowl until soft peaks form.
Use a large serrated knife to split the cake. Place 1 cake layer in the base of a glass serving bowl. Drizzle with half the liqueur, if using. Spread with half the blackberry jam. Spoon over half the mascarpone mixture and half the remaining lemon curd. Sprinkle with half the blackberries and meringues. Continue layering with remaining cake, liqueur, jam, mascarpone mixture, lemon curd, blackberries and meringues.