Make the Custard: In a saucepan, whisk together the eggs, sugar, and starch. Gradually whisk in the cold milk. Heat the mixture over medium heat, whisking constantly, until it thickens and begins to bubble. Remove from heat and stir in the butter and vanilla essence. Let the custard cool slightly.

Prepare the Coffee Layer: While the custard cools, dissolve the instant coffee in the warm milk. Stir well to ensure the coffee is fully incorporated.

Assemble the Cake: Line a springform pan or baking dish with plastic wrap. This will help with easy removal later.

Dip and Layer: One at a time, dip the cocoa biscuits (ladyfingers) briefly into the coffee mixture. Don't over soak them, or they will become mushy. Arrange the dipped biscuits in a single layer on the bottom of the prepared pan.

Custard and Chocolate Layers: Pour half of the cooled custard over the biscuit layer. Top with another layer of dipped biscuits. Pour the remaining custard on top. Spread the chopped Milka chocolate evenly over the final custard layer.

Refrigerate and Set: Cover the pan tightly with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, to allow the cake to set completely.

Serve: Before serving, whip the whipping cream until stiff peaks form. Spread the whipped cream over the top of the cake for a beautiful finishing touch. Decorate with additional chopped chocolate or cocoa biscuits, if desired.