Combine 1½ cups crushed digestive biscuits, ½ cup desiccated coconut, ¼ cup sugar, and 5 tbsp melted butter. Press into a pie tin and bake at 180°C for 10 minutes. Cool completely.
In a pan, warm 1 can coconut milk, 1 cup milk, ½ cup sugar, and ¼ cup corn flour. Stir until it thickens. Add ½ tsp vanilla and ¾ cup coconut. Cool for 10 minutes.
Fill the coconut mixture into the crust. Smooth the top and refrigerate for a minimum of 3 hours or until set. Don't be in a hurry with this step—firm filling is important.
Whip 1 cup cold cream with 2 tbsp powdered sugar until stiff peaks. Spread or pipe on the chilled pie. Apply strokes lightly to maintain airiness.
Melt 50g Bournville chocolate with 1 tbsp cream. Drizzle over generously. Allow it to set for 10 minutes before serving.