Place biscuits into TM bowl and chop 2 sec/speed 5 or until roughly chopped. Set aside.
Add egg whites, a pinch of salt and sugar to bowl. Mix 1.5 min/37°C/Butterfly/speed 3.5/MC OFF.
Scrape down the sides. Add 50g of the icing sugar and continue to beat for 1 min/speed 3.5/MC OFF. Scrape down sides and repeat.
Set aside the meringue in a large bowl.
Clean and dry the TM bowl. Melt the butter for 3 min/60°C/speed 2. Ensure butter is completely melted otherwise continue melting.
Add the remaining icing sugar (150g), cocoa, vanilla, liquor if using and mix 1 min/speed 3. Whilst mixing, add the egg yolks through the hole in lid.
Scrape down sides then add the crushed biscuits back into the bowl and mix 15 sec/Reverse/speed 1.
Add the biscuit mixture to meringue and gently fold together.
Line a baking tin with enough cling wrap to hang over the sides. Pour the mixture into the tin and cover the top with the excess cling wrap. Grab the two ends of cling wrap and take the mixture out of the tin. Roll it on the bench to form a log shape. Set in freezer for 1-2 hours to harden.
Once the log has hardened, slice it into pieces and serve with tea and coffee. Or store in the fridge or freezer until ready to serve.
Try adding some sultanas, coconut, goji berries, chopped nuts or cranberries to change it up if you like. Add in step 7 along with the crushed biscuits or try sprinkling some on top before cutting into slices.