Preheat the oven to 325 degrees F.
Add the oil to a heavy skillet or Dutch oven over medium heat. Stir in the onion and shallots and sauté for about 20 minutes until they are softened and browned. Add in the ginger and garlic and cook for 1-2 minutes more.
Remove the pan from heat and stir in the vadouvan.
Transfer the mixture to a parchment lined baking sheet and spread it out into a single layer. Bake for about an hour, stirring occasionally. The Vadouvan paste is done when most of the moisture has evaporated and it is the consistency of a thick, sticky paste.
Allow to cool, and store in an airtight container, refrigerated, until ready to use. Vadouvan paste stores well in the refrigerator up to one month.
Notes:
- We used one pound yellow onions and one pound red onions, but any combination is just fine. Some recipes call for using a food processor on the onions and shallots but we like the texture from hand chopping better. - Fresh or dried curry leaves and/or turmeric are a wonderful addition to this recipe if they are available in your area.
Adapted from Epicurious.