To the remaining ⅓ cake batter, add the 1 teaspoon of cardamom, then spread into the prepared springform pan.
Spread the chocolate batter over the cardamom batter. (Using a piping bag is easiest, otherwise drizzle.) Repeat with the pistachio cake mix, again using a piping bag, if available. Using an offset spatula, marble the batter, using a figure-8 pattern, driving the spatula all the way to the base of the pan and dragging through the batters.
To make the crumb topping: In a small bowl, combine the brown sugar, flour, cocoa powder, melted butter, cardamom and salt with a spoon or by hand, until it resembles crumbled Oreos or dirt. Evenly distribute topping on top of cake.
Bake the coffee cake for about 35 minutes, until center is just set.
Meanwhile, prepare the ganache. Combine the warmed heavy cream and the chocolate, until a smooth ganache is formed.
Remove cake from oven, and drizzle liberally with chocolate ganache and additional pistachio cream and top with knafeh and crushed pistachios.
