Whisk together the egg whites until they form stiff peaks then add the sugar in spoonfuls. Keep going until the meringue becomes glossy and thick - take a pinch and rub it between your fingers; if it's still grainy, keep whisking! Spoon roughly onto a lined baking tray and bake for around 2 hours, then break it up into small chunks. It helps having two ovens at this point - if you do, whack the second up to 180°C.
Sift the flour and bicarb into a large mixing bowl. Make sure the butter is soft and lightly rub into the flour with your fingertips, until the mixture resembles coarse, fine breadcrumbs.
Whisk through the sugar until fully incorporated then make a well and pour in the buttermilk and vanilla. Stir in everything to make a sticky dough - add splashes of milk if it looks too dry.
Turn the dough out onto a lightly floured surface and gently form into a disk. Place it in a lined 23 cm spring form tin. Bake for around 30 mins before covering with silver foil to prevent the top burning. Check it with a skewer for doneness and leave it to cool for at least an hour - it'll need to be really cold for the next step.
Whisk the clotted cream with the icing sugar and cream of tartar. Add the double cream and whisk to stiff peaks.
To assemble the scone cake, carefully cut in half horizontally. Spread the bottom half with a layer of strawberry jam, followed by the whipped cream, fresh strawberries and pieces of broken up meringue.