Wash the meat under running water and drain. Transfer to a pot, and add 8 cups of water and cook on high heat. Spoon the scum as it appears on top, and once it reaches a boiling point add the whole onions. Cover the pot, reduce heat to low and simmer for 2 hours until the meat is fully cooked. Strain the broth and transfer the meat to a dish to cool down. Shred the meat.
Remove the cooked onions and blend using a hand blender, then transfer to a large pot. Add 1 1/2 cups of the meat broth to the onions. Stir in the yogurt and the diluted cornstarch and season with salt.
Cook over high heat whisking continuously; when the mixture reaches a boiling point, add the cooked meat shreds, and simmer over medium-low heat.
Meanwhile melt butter in a skillet over medium heat, and sauté the pine nuts, stirring constantly to a golden color.
Transfer the pine nuts to the yogurt mixture, simmer for a bout 5 minutes over low heat, serve with rice and vermicelli.