Melt the butter in a small saucepan over medium heat. Add the flour and stir continuously for about a minute until smooth.
Add the taco seasoning and tomato paste and stir until the tomato paste is incorporated and the mixture is smooth. Add the lime juice.
Slowly add the chicken stock, a little at a time, stirring as you go. Continue adding stock until you have a smooth, pourable sauce, you may not need all of it. Let it simmer for a couple of minutes, then taste and adjust the seasoning as needed.
Heat a little olive oil in a large skillet over medium-high heat. Add the ground beef and cook, breaking it apart as it cooks, until it's deeply browned and crispy in spots.
Add the taco seasoning and stir to coat the beef. Add the black beans and a splash of water, then stir everything together and cook for another couple of minutes until the mixture is nicely combined and seasoned. Taste and adjust with more taco seasoning or salt if needed.
Preheat your oven to 400°F.
Spread a small amount of enchilada sauce over the bottom of a baking dish.
Take a tortilla and spoon the beef and black bean mixture down the centre. Add some chopped yellow onion and a generous handful of shredded cheese. I like using half cheddar and half mozzarella.
Roll the tortilla tightly around the filling, but don't fold in the ends. Place it seam-side down in the baking dish. Continue with the remaining tortillas, arranging them snugly side by side until the dish is full.
Pour the remaining enchilada sauce over the top, but don't completely smother the tortillas. Leaving some of the tortilla exposed gives you those delicious crispy edges. You may not need all the sauce.
Top generously with more shredded cheese and scatter sliced jalapeños over the top.
Bake at 400°F for about 15–20 minutes, or until the cheese is melted, bubbling, and beautifully golden and the exposed edges are crispy.
Let the enchiladas cool for a few minutes, then top with a little freshly cracked black pepper, a dollop of sour cream, guacamole, and plenty of fresh cilantro. Finish with fresh lime juice.