Preheat oven to 200°C (180°C fan-forced). Grease a 25cm x 35cm swiss roll pan; line with baking paper.
Place biscuits in a single layer in pan (trim to fit if necessary).
Combine butter and sugar in a medium saucepan over low heat. Cook, stirring, for 2 minutes or until butter melts. Increase heat to high; cook, stirring, 5 minutes or until sugar dissolves and mixture is well combined and bubbling. Remove from heat; pour evenly over biscuits; spread to cover.
Bake for 12 minutes or until golden. Remove from oven; sprinkle evenly with chocolate. Return to oven for 1 minute or until chocolate melts.
Using a palette knife or the back of a spoon, smooth chocolate. Immediately sprinkle with hundreds and thousands.
Stand for 1 hour or until the chocolate is set. Using a large kitchen knife, cut bark into large shards to serve.
Bark will keep in an airtight container for up to 1 week.