Rogan Josh, Lamb Shanks in the Slow Cooker

2/3 cup sour cream
1 tablespoon plain flour
1/2 teaspoon chili powder
1 teaspoon ground coriander
1/2 teaspoon ground ginger
2 chicken stock cubes
4 whole cardamom pods, broken
1 can diced tomatoes
1 cup water
ground nutmeg to taste
salt and ground black pepper to taste
2 tablespoons corn flour
1/4 cup water
1 large onion, cut into wedges
3 lamb shanks
1 carrot, diced
2 potatoes, diced

Stir the sour cream and all-purpose flour together in a small bowl until smooth and set aside.
In a separate small bowl, mix together the cornstarch and water to make a paste.
Combine the chili powder, coriander, ginger, stock cubes, cardamom, tomatoes, water, nutmeg, salt and pepper in a medium saucepan; bring to a boil over high heat. Slowly add the cornstarch paste to the tomato mixture, stirring constantly; simmer for 2 minutes. Remove the saucepan from the heat and slowly stir in the sour cream and flour mixture.
Arrange the onions across the bottom of a slow cooker, lay the shanks on top of the onions and pour the prepared tomato mixture over the meat. Place the carrots and potatoes on top of the sauce.
Cover and cook in the slow cooker on High for 8 hours.