This is one of my favorite curries. I invented it as a way to get that wonderful intense curry taste without meat and it is excellent. You can control the heat by reducing the cayenne pepper or using a bit less curry paste. 

Ingredients

2 Tbsp Oil
1 large Onion, chopped
4 cloves Garlic, chopped
1  inch piece of fresh Ginger, grated

2 Medium Sweet potatoes, peeled and cut into 1 inch cubes
1/2 cup Tomatoes, crushed

3-4 Tbsp Curry Paste, Pataks is one of the best. I use the Madras Paste.
1/4 tsp Cardamon, ground
1/4 tsp Cinnamon, ground
Pinch of Cloves, ground
1 tsp Garam Marsala
1/2 tsp Cayenne Pepper, ground
4 Curry Leaves
1/4 tsp Coriander, ground

1/4 cup shredded sweetened Coconut
Juice of one Lemon
Salt and Black  Pepper to taste
Water, as needed.

Begin by placing the onion, garlic and ginger into a food processor and pulse until it is puréed. I have a mini food processor I use for this.

Then heat your oil in a pan which has a lid and once the oil is hot, add your purée and some salt and pepper and sauté it for 7-10 minutes.  Then add your curry paste and spices and sauté for 3-4 minutes.

Add your sweet potatoes and the rest of your ingredients and put on the lid and bring to a simmer. At this point you may add a little water if the curry is too thick, but not too much water. You want it to be the consistency of a stew not a soup.

You can continue cooking for 45 minutes covered on the stove top or you can finish it in a preheated 325 degree oven for 35 minutes.  You just need to make sure the sweet potatoes are cooked through.

Remove from heat or oven and allow it to sit covered for 5 minutes and serve with naan bread and basmati rice.