Measure the sour cream, heavy cream, instant pudding, dry milk (if using), and vanilla extract in a large mixing bowl. Use an electric mixer or the whisk attachment until you have a thick creme.
Dip the tea biscuits in the cold milk and line them in an even layer over the bottom of your serving dish.
Spread half of the cream over the cookies.
Place another layer of milk-soaked biscuits over the cream, then spread the rest of the cream.
Top with a third layer of milk-soaked cookies.
Place the chopped chocolate in a medium bowl and pour over the heavy cream.
Warm in the microwave (or over a double boiler), using 15-seconds increments warm the chocolate 2-3 times, stirrig between each time until the chocolate has melted.
Gently stir until you have a smooth chocolate ganache.
Pour the ganache over the top of the cake, sprinkle with crushed cookies, and refrigerate for a minimum of four hours.