If making your own, make the honeycomb as described in my recipe and let set for 45mins - 1 hour before using.
Preheat the oven to 200C/180C Fan/Gas 6. Line an 8′ Square Baking Pan (9″ will work for thinner bars) with baking parchment.
In a large bowl, or the bowl of a stand mixer, combine the butter, brown sugar and granulated sugar (medium speed) for about 3-5 minutes until fully combined.
Add the egg and vanilla and mix again.
Fold in the flour, baking soda and cornflour and fold together. Then gently fold in the chocolate and crushed honeycomb (or chopped Crunchie bars if using)
Press into the prepared tin. The dough should be pretty solid so may require a bit of work to really press into the edges (I use clean hands).
Bake for about 25 minutes, until entirely baked. Leave to cool on a wire rack for at least 45 minutes before attempting to cut (they retain their heat and will fall apart if cut any earlier).