Heat the oil in a medium saucepan over medium-high heat. Add the onions and garlic, and cook until soft. Add the chiles and stock, and bring to a simmer for 20 to 25 minutes, or until the chiles are soft. Transfer the mixture to a food processor and process until smooth.
Strain the mixture into a saute pan that has been set on high heat for a few minutes, and cook the sauce until slightly thick. Remove from the heat and stir in the creme fraiche and maple syrup. Season with salt and pepper, to taste.