Preheat the oven to 180 °C (350 °F) and line a rectangular cake tin (35 x 28 x 7 cm) with oil and baking paper. Prepare the chocolate cake mix according to the instructions on the box. Pour the cake batter into the prepared pan and bake for 25-30 minutes. Allow to cool on a wire rack.
Gently melt the chocolate in a heatproof bowl in the microwave in 30-second increments, stirring often. Once melted, add this to the custard and stir to combine. Set aside.
To make the whipped cream, add the cream and icing sugar to a bowl of a stand mixer fitted with a whisk attachment, and beat until soft peaks form. Set aside.
Slice the cooled cake into cubes of about 3cm (1.2inches) and create a layer of cake at the bottom of the trifle dish. Dot the strawberries, sliced and stewed cherries, in between the cake pieces.
Spoon a layer of chocolate custard over the cake layer. Add a layer of cream on top. Continue layering the trifle with cake, fruit, custard, and finally cream, until you have used up all the ingredients.
Finish with the remaining cream, then top the trifle with grated chocolate and whole fresh cherries. Serve and enjoy!
Notes
Use room temperature custard so the melted chocolate incorporates into the custard easily.
I have mentioned the eggs and oil in the recipe card, as you will most likely need these to make the cake mix, along with water.