Heat 1 tablespoon of olive oil in a deep pot over medium heat.
Add the onions and saute until the onion is soft, 4 to 5 minutes.
Add the garlic, brown sugar, cumin, and oregano and cook 1 minute more.
Add the sherry, chipotle chili, adobo sauce, tomatoes and vegetable broth.
Bring to a slow boil then simmer for about 20 minutes, until the sauce has thickened to stew consistency.
Puree with an immersion blender and set aside to cool.
This sauce can be made in advance and stored up to 3 days in the fridge and 3 months in the freezer.
Store sauce in an airtight container and defrost before using if stored in the freezer.
For the Enchiladas
In a large frying pan heat the ½ cup olive oil over medium high heat.
It’s ready for frying when a small bit of tortilla sizzles immediately when added to the pan. Fry each corn tortilla for about 5-8 seconds per side, turning with tongs. Place the fried tortillas on a plate lined with paper towels to drain.
In a medium bowl combine the black beans, spinach, corn, cumin, salt and black pepper. Mix to combine well.
Spoon half of your enchilada sauce on the bottom of your slow cooker.
Divide the filling among the 12 tortillas, spooning about 2-3 tablespoons worth of the bean mixture down the center of each tortilla.
Sprinkle with about 1-2 tablespoons of Monterey Jack cheese, then roll up and place in your slow cooker, seam-side down.
Use the same method for the remaining tortillas, pressing each filled and rolled tortilla snuggly up against the others when placing them in your slow cooker. I can usually get 10 filled tortillas across and two filled tortillas in the empty space on either side of my row. If your slow cooker is smaller than mine and this isn’t possible, you can always do a second row of filled tortillas on top of the first. Just spoon a few tablespoons of sauce between the layers.
When all of the tortillas have been placed in the slow cooker ladle the rest of the enchilada sauce on top of them and sprinkle with the double cheddar cheese.
Cook for 2½ hours on high or 4½ – 5 hours on low.
If you would like to make these enchiladas in the oven you can do so by assembling them into a large baking dish, covering with aluminum foil and baking them for 25 to 30 minutes at 400 degrees F.