In a blender, combine ripe mango chunks, laban or yogurt, regular milk, a small pinch of salt, and cardamom powder if you're using it. Blend until smooth and pourable. If the mixture is too thick—which can happen depending on your fruit and yogurt—add a little more milk and blend again.
Note on Yogurt vs. Laban: Laban (a thinner, drinkable yogurt common in Middle Eastern grocery stores) is ideal for this recipe. If you can’t find it, substitute with regular (not Greek) yogurt, but use only half the amount and increase the milk to adjust the consistency. Taste the mix and tweak it based on your preferences.
When the cake is done baking, take it out of the oven and poke holes all over using a toothpick. Pour the mango lassi milk generously over the warm cake, keeping a bit aside to serve with the final dish.
Let the cake rest at room temperature for about 30 minutes so it can absorb the milk, then refrigerate for a minimum of 4 to 6 hours—or overnight for best results.
Make the sweetened whipped cream: Whip whipping cream, icing sugar, and vanilla until it reaches stiff peaks.
Just before serving, spread a layer of whipped cream over the top and finish with a generous sprinkle of fresh mango chunks and chopped pistachios. Serve chilled, with the extra mango milk on the side for an extra hit of flavor.