Put the egg whites and cream of tartar in the bowl of an electric stand
mixer. Using the whisk attachment, whip the egg whites on speed
8 (under high) for about 3 minutes until they change from foamy to
stiffish and white. Start adding the caster sugar gradually – around
2 teaspoons at a time over 3 minutes, until the meringue is shiny
and taut.

Take the bowl off the mixer and tip the nut mix in. Fold in lightly with
a stiff spatula so there are no white streaks in the batter.

Scrape the batter into the prepared cake tin and smooth the top
out evenly. Bake for 40–45 minutes, until the top crust is the palest
brown and feels crispy, then turn the oven off and leave the door ajar
for the layers to cool down slowly for 1 hour. Remove and leave in the
tin to cool to room temperature.

If making the cake the day before assembly, leave it with a dry tea towel
(dish towel) on top, or pop it back in the cooled down oven. Don’t wrap it, or
it will get sweaty and soft.

While the meringue is cooling, prepare the Lazy toffee crunch and
make the buttercream. Make the crème fraîche whip by whipping the
cream and crème fraîche until billowy soft. Keep chilled. When the
toffee crunch has cooled, crush it in a mortar and pestle (or chop
coarsely) and mix 100 g (3½ oz) of the crunch with 350 g (12½ oz)
of the buttercream. (Add a splash of rum or coffee too, if you want a
little spike of something something!) Reserve the remaining crushed
crunch in the freezer for topping the ganache next day.

To assemble, gently invert the meringue from the tin onto a large
chopping board. Peel the paper away. Trim the short edges, then
cut with the utmost precision (and a sharp serrated knife) into three
equal tiles. Choose your layers now: the most even tile should be
your top, so leave this one bottom up. The remaining two will be your
middle layers, so gently flip those to bottom crust down.*