Crush the biscuits in a resealable bag with a rolling pin, or any other blunt instrument you can do serious damage with, until you have fine crumbs.
Melt the butter in a large saucepan then add the biscuit crumbs and mix to combine. Tip the butter and biscuit mix into the base of a 20cm springform tin and press down with the back of a spoon so it covers the base and goes 5cm up the sides of the tin to form a crust. Cover and place in the fridge to chill while you prepare the rest of the ingredients.
Place the chocolate in a heatproof bowl then set it over a small saucepan of barely simmering water, making sure the base of the bowl does not touch the water, and gently melt, stirring occasionally.
In a free-standing mixer fitted with the whisk attachment - or using an electric hand whisk - beat the cream cheese, cream, and mascarpone together until the mixture becomes very thick and almost mousse-like.
Beat in the white chocolate and lemon zest until just combined. Finally ripple in half the lemon curd.
Spread the mixture evenly over the top of the biscuit base, lightly spread over the remaining lemon curd then cover and place in the fridge to chill and set for at least 3-4 hours.
For the meringue, grab yourself a large, clean bowl or use a freestanding mixer and beat your egg whites to stiff peaks. Meanwhile place the sugar and water into a large saucepan and stir gently until the sugar has dissolved. Once dissolved immediately stop stirring to avoid crystallisation. Raise the heat and bubble until the sugar reaches 115°C -120°C on a thermometer. Once the temperature is reached start whisking again and slowly trickle the sugar syrup into the egg whites being careful to avoid the beater. Once all is incorporated, add the cream of tartar, salt and beat again for 7-10 mins or until thick, shiny and the bowl is no longer hot.
Remove the cheesecake from the tin and top with billows of the meringue. Use a blow torch to lightly brown the meringue to get that iconic lemon meringue pie look, then slice with a hot knife.