Prepare the filling: Heat olive oil in a heavy-based pan over medium heat. Add onion and capsicum; sauté 5 minutes until soft and translucent.
Add beef mince; cook until browned, breaking it up as it cooks. If your meat was particularly watery, drain off the excess before continuing — this helps the mixture stay rich and thick rather than watery.
Stir in garlic, cumin, paprika, chilli powder, oregano, and cayenne; cook 1-2 minutes until fragrant.
Add crushed tomatoes, water, salt, and 1 tbsp sugar. Simmer 10–15 minutes until thickened.
Taste and adjust (I added another 1 tbsp sugar, extra salt, and pepper).
Stir in black beans and corn; cook 5 minutes more, then remove from heat and let cool slightly.
Toast the base tortilla: Heat a dry pan over moderate heat; toast one tortilla until lightly firm.
Prepare the pan: Lightly grease a 20–23 cm springform pan with spray oil (no baking paper). The tin you use will depend on the size of your tortillas; it should fit snugly.
Assemble: Place toasted tortilla in base.
Sprinkle a little cheese to create a barrier.
Spread one-third of the mince mixture over (or less if you're making a 6-tortilla stack).
Sprinkle a little cheese and jalapeños (if using).
Repeat layers, finishing with a tortilla on top.
Spread sour cream over the top and finish with cheese.
Bake: 170 °C fan (190 °C conventional / 375 °F) for 20–30 minutes, until golden and bubbling. Run a thin knife around the inside of the tin to release any cheese that may have stuck.
Rest: Cool 20-30 minutes before releasing the springform pan and slicing.