In a blender, add the yogurt and cornstarch, and mix on high speed until thoroughly incorporated. Pour the mixture into a medium-sized saucepan over medium-low heat and stir until it comes to a simmer, then sample to make sure it doesn't taste like cornstarch. Once the cornstarch flavor is gone, remove from the heat and set aside.
With a colander, strain the lamb while reserving the broth. Season with the remaining 2 tablespoons of salt and mix to integrate gently.
Add the cooked lamb to the yogurt sauce along with 7 ounces of the reserved stock. Bring to a simmer.
Serve in shallow bowl with roast pine nuts over the top.