Place the basmati rice in a large bowl and cover with hot water. Set aside.
Wash the garlic head. Cut about a quarter inch off the top to expose the cloves. Set aside.
Lightly toast cumin, coriander seeds and peppercorns in a pan for a few minutes. (Take care that they do not burn)
Grind using a mortar and pestle or a spice grinder. Set aside.
Heat oil in a large dutch oven over high heat. Add the lamb pieces, stir occasionally until the lamb is browned all around.
Remove the lamb pieces and set aside.
Stir in onions and cook, until onion is soft and golden, about 10 minutes.
Stir in carrots and cook, until carrots are tender, about 10 minutes.
Add the lamb and mix.
Sprinkle the mixture of cumin, coriander, peppercorns and add the barberries.
Add the whole garlic head, mix well. Reduce heat to medium. Cover and cook for 30 minutes.
Wash and drain the basmati rice. Pour the rice over the lamb mixture in an even layer.
Slowly pour the vegetable broth in. The rice should be covered in liquid by about ½ inch. Do not stir.
Season with salt and reduce heat to medium-low. Cover and cook until rice is tender and liquid has been absorbed, about 20 minutes.
Mix the ingredients as you serve the dish on a platter. Garnish with the garlic head.