Make the marinade:
Put all of the seeds and whole spices in a cold pan and gently warm it to toast them briefly, about 2 to 3 minutes. Do not burn the seeds and whole spices.
Remove the seeds and spices from the pan a let them cool
Put all of the dry ingredients, (seeds whole spices, chilies) in a blender and blend until the whole mix is a powder.
Add the liquid (vinegar, water, tamarind concentrate), garlic, and ginger and puree until it is a nice homogenous paste.
I’m convinced that you can get very close results by just using ground spices instead of whole, you just need to adjust the measurements. Actually, for consistency purposes, ground spices always from the same source might be better. It will always be the same. As cooks we rely on consistency. We never want a dish to be a one hit wonder.
Cut the lamb into stew sized chunks. I like about an inch. You are going to cook this for 2 to 2 ½ hours so you don’t want the lamb to disintegrate. Be sure to remove excess fat. You can leave a bit of fat for flavor, but trim the excess.
Mix the lamb chunks with the marinade and refrigerate overnight.
Start making the vindaloo 4 hours before you want to serve.
Cut the onion into a medium to fine dice.
Warm the Dutch oven over medium heat and add the olive oil.
Add the onions and a sprinkle of salt and pepper
sauté the onions until they start to get color
Add the turmeric and the Kashmiri chili and sauté about a minute longer until they blend and release aromas.
Add the marinated lamb with all of the marinade, and stir it up.
Sauté the lamb for a few minutes occasionally stirring.
Add the water and bring to a simmer.
As soon as it starts simmering, stir it up, put the lid on, and put it on low on the back burner.
Stir every ½ hour.
At the 1 ½ hour mark, position the lid to allow evaporation, so leave about a ½ inch crack in the top of the pot by shifting the lid.
Keep an eye and keep stirring. Raise the heat to a low medium to accelerate reduction. Keep an eye and keep stirring. You don't want it to burn or stick to the bottom.
It is done when the lamb is tender and the gravy is thickened and homogenous. You should not see any chunks of onion; it should be lamb in a reddish-brown gravy.
Add the sugar. Add the salt one teaspoon at a time and test for seasoning. Add pepper to taste.
People like it with rice, but I’m a bread guy. Plain naan or any type of baguette. I bet a Portuguese roll would also be fantastic, consider the heritage.