Preheat your oven to 350°F.
Grease a 9-inch deep-dish pie plate.
Crush the digestive biscuits in a freezer bag using a rolling pin until fine.
Mix with melted butter, then press the mixture into the pie plate to form the crust.
Bake for 10 minutes.
Melt dark chocolate in a saucepan over low heat.
Stir in heavy cream until smooth.
Remove from heat.
In a bowl, whisk sugar and beaten eggs together.
Slowly add in the melted chocolate mixture, stirring constantly.
Add vanilla extract.
Pour the chocolate filling into the crust.
Bake for 20 minutes or until set.
Cool completely, then refrigerate for at least 2 hours.
Whip the cream until stiff peaks form.
Spread over the chilled pie before serving.