To a bowl add all the ingredients listed under "to marinate". Make sure the yogurt that you use here is thick. Whisk to combine everything together.
Trim the outer leaves and stalks of the cauliflower but make sure the head remains intact. Coat the entire cauliflower with the marinade. Use you hands to spread the marinade all over, going to sides and also to the back of the cauliflower.
Cover and refrigerate for a minimum of 1 hour. If you have time, you can even marinate 4-6 hours or even overnight.
Once you have marinated the cauliflower with the masala for a desired amount of time, roast it in the oven at 400 F degrees for 45 to 50 minutes on until tender (a smaller head might get done in less time and a bigger one will take more time so adjust accordingly).
Meanwhile make the sauce. Heat oil in a pan on medium heat. Once the oil is hot, add the cumin seeds and let them sizzle. Then add the onion and cook for 2-3 minutes till soft and translucent.
Add ginger garlic paste and cook for another minute or two till the raw smell goes away. Add the chopped tomatoes along with store bought tomato puree, salt and 1/4 cup of water. Let the tomatoes cook for 3 minutes.
Add red chili powder, curry powder, sugar and let the masala cook for 2 more minutes.
Once the masala is nicely cooked, add the remaining 3/4 cup water to the pan. Mix everything well and then blend the mixture to a smooth paste.
Transfer the pureed mixture back to the pan and add butter and chopped cilantro. Let it all simmer for 2 minutes.
Place the roasted cauliflower in the center of the serving plate and pour the prepared sauce all around the cauliflower.
Serve roasted cauliflower tikka with onion rings and cilantro-mint chutney on the side!
You may serve this cauliflower tikka without the sauce. Serve it with cilantro chutney and it would make a great appetizer. With the sauce, it's more of a complete meal.
I strongly recommend using store bought puree here. But if you can't get it, make a puree of 2 tomatoes and use in the recipe.
A smaller cauliflower head might get done in less time and a bigger one will take more time so adjust the timing accordingly.