I would like to suggest that the sweet fragrance you mention is probably primarily coriander seed powder. Coriander powder is, to my knowledge, usually the major component of garam masala, as well as in other commonly used ground masalas like sambar powder. Coriander powder is used in volume, not only because of its magical citrus-honey scent but also its mildness and lack of bitterness compared to other spices. Both garam masala and coriander powder are added to those creamy gravy curries. Other sweet-smelling spices such as cinnamon (which may be the secondary source of sweet aromas, or the main source in curries that don't have coriander), cardamom and nutmeg are also usually included in garam masala.
The actual sweetness and creaminess of such curries meanwhile, usually comes from fried onions and either cashews and/or dairy products. Instead of (or in addition to) onion, ground coconut may be used. White poppy seeds and/or watermelon seeds are also used in some creamy sauces.
Here is a sort of general recipe for a rich creamy gravy curry sauce like the one for paneer butter masala:
- 1 tbsp ghee (or, since I'm vegan I use 2 tsp coconut oil and 1 tsp olive oil)
- 1/4 tsp cumin seeds (optional)
- 1 clove, crushed (optional)
- seeds of 1 cardamom, crushed (optional)
- 1 Indian bay leaf (optional)
- 1 green chilli, chopped
- 1 red onion, roughly chopped
- large handful cashew nuts (about 10-12)
- 1 tsp fresh ginger, roughly chopped
- 1 tsp fresh garlic, roughly chopped
- 1/2-1 tomato, chopped (about 2-3 tbsp chopped)
- salt to taste
- 1 tsp coriander powder
- 1/4 tsp garam masala
- red chilli powder to taste (optional)
- 1/3 cup thick curd/yogurt or cream (since I'm vegan I use cashew almond curd)
- 1/2 tsp dried fenugreek leaves (kasuri methi)
- Fry the cumin, bay leaf, clove and cardamom for a few seconds
- Add onion and chilli and cook until the onion is turning brown
- Add cashews, ginger and garlic and cook for a minute
- Add the tomato with salt and cook until the tomato turns totally mushy
- Add coriander, garam masala and chilli powder if wanted. Take off the heat and allow to cool somewhat, at least so it's not steaming hot. Remove the bay leaf.
- Grind the mixture to a paste and return the paste to the heat until it starts to simmer.
- Add curd or cream and kasuri methi
Sauce is ready: add paneer, cooked veggies or whatever.
I make garam masala similar to Richa Hingle's recipe which has:
- 1/2 cup (40 g) whole coriander seeds
- 1/4 cup (25 g) cumin seeds
- 6 to 8 (6 to 8 ) 2-inch cinnamon sticks
- 8 to 10 black cardamoms
- 2 tablespoons green cardamom pods
- 2 tablespoons cloves
- 1 tablespoons (1 tablespoons) black peppercorns
- 10 to 12 Indian bay leaves
- 1 nutmeg optional
P.S. I can heartily recommend Dassana Amit's recipe blog. You may find this dhaba style recipe of hers helps you figure out the magic formula.