Line a 20cm loose-bottom cake tin with baking paper.
Process biscuits in a food processor until fine.
Add butter and process until mixture resembles wet sand.
Press into prepared tin, forming a 1cm-thick layer. Refrigerate for 20 minutes.
Heat sugar and cream in a saucepan. Stir over a low heat until sugar dissolves.
Bring to the boil and cook until slightly thickened, about 15 minutes.
Remove from heat and add chocolate. Stir until it is melted and mixture is smooth.
Add egg yolks and mix.
Return to a medium heat and stir for 10-12 minutes until mixture thickens.
Remove from heat and cool slightly. Stir in vanilla.
Pour over biscuit crust and set aside to cool.
Refrigerate until firm.
Sprinkle with peppermint crisp shards, slice and serve.