Brown the chicken: Heat 2 large skillets over high heat. Add half of the oil to each. Arrange the chicken on a tray in a single layer and season with salt. Turn the pieces over and season the other side. When the oil begins to smoke lightly, carefully add the chicken, skin side down, to the skillets, leaving space between each piece of chicken. Reduce the heat to medium and allow the chicken to brown on their first side, 5 to 8 minutes. Resist the temptation to move or turn the pieces. Use metal tongs to carefully turn the chicken pieces to their second side and brown 3 to 5 additional minutes. Transfer the chicken pieces to a tray and set aside.
Prepare the garlic: Grate 6 of the cloves of garlic and set aside for the sauce. Cut the remaining 12 cloves in half lengthwise.
Make the sauce: In one of the skillets you cooked the chicken in, add the cumin and coriander and stir rapidly over medium-low heat to give them a quick toast, 10 to 15 seconds. Immediately add the onions and grated garlic. Season with salt and cook over medium heat, stirring frequently, until the onions turn light brown, 3 to 5 minutes. Add the cinnamon stick, pepper flakes, bay leaves and tomatoes. Allow the tomatoes to cook, breaking them apart with a spoon as they cook, 8 to 10 minutes, and then add 1 cup water.
Toast the garlic cloves: In the other skillet the you cooked the chicken in, arrange the garlic halves in a single layer in the cooking grease. Toast the garlic over low heat until golden brown and crisped, 10 to 12 minutes. Remove the garlic from the skillet, sprinkle with salt and drain on a kitchen towel.
Finish cooking the chicken: Arrange the chicken pieces, skin side up, in the sauce. Cover the skillet, keep the heat low and continue cooking until the pieces are cooked through, 25 to 30 minutes. Remove the cover and stir in the ginger, cream and vinegar. Cover and simmer 2 to 3 additional minutes.
Test the center of a thigh to make sure the chicken is cooked through. It should reach an internal temperature of 165 degrees F and the juices should run "clear," not pink. Remove and discard the cinnamon stick and bay leaves. Taste and adjust the seasoning. Top with the toasted garlic and serve immediately.