Warm the butter, brown sugar, vanilla, milk and biscuit crumbs in saucepan and stir until combined.
Line baking pan with baking paper.
Layer the base with biscuits. Pour half of the mixture over the base. Layer chocolate chunks and marshmallows on top. Add another layer of biscuits, the rest of the mixture, chocolate chunks and marshmallows. On the top put chocolate chunks and marshmallows.
Bake in oven for 15 minutes until combined together. Allow to cool before cutting into 9 pieces. Serve warm with ice cream for a special treat!
This recipe has been edited to include measures and ingredients more familiar to Australian and New Zealand cooks.