Combine all ingredients in a medium saucepan over medium heat. Whisk until smooth. When mixture comes to a boil, reduce heat and slimmer for 20 minutes, stirring often. Remove pan from heat and cover until cool.
Mash the beans to a textured pur e with a food processor or potato masher. Transfer to a bowl and stir in the onion, chiles, cumin and salt. Using 1/4 cup of the bean mixture, make 3 x 1/2-inch patties.
Heat 2 tablespoons of the oil in a large heavy skillet. Put as many patties in the skillet as will fit in a single uncrowded layer and fry over fairly high heat until golden and toasted, about 1 minute per side. Transfer to a platter. Fry remaining patties.
Sprinkle each patty with salsa, then drizzle Crema over. Serve immediately.