Roast the Chiles: Preheat your grill to its highest setting. Place the poblano chiles on a baking tray and grill them for 5-7 minutes per side, turning occasionally until the skin is blackened and blistered all over. Transfer the hot chiles to a bowl and cover tightly with cling film. Let them steam for 10-15 minutes. This makes the skins incredibly easy to peel off.

Prepare the Chiles: Once cooled, gently peel the blistered skin from the chiles; it should slide off easily. Make a slit down one side of each chile and carefully remove the seeds and membranes. Lay them flat, ready for layering.

Cook the Filling: While the chiles are steaming, heat the olive oil in a large frying pan over a medium-high heat. Add the chopped onion and cook for 5 minutes until softened. Add the minced garlic and cook for another minute until fragrant.

Brown the Mince: Add the beef mince to the pan, breaking it up with a wooden spoon. Cook until it's browned all over, about 6-8 minutes. Drain off any excess fat. Stir in the cumin, smoked paprika, oregano, salt, and pepper. Cook for one minute more to toast the spices.

Create the Sauce: Pour the tinned chopped tomatoes and tomato purée into the pan with the beef. Stir everything together, bring to a simmer, then reduce the heat and let it bubble gently for 10 minutes to allow the flavours to meld.

Assemble the Casserole: Preheat your oven to 180°C (160°C fan). Spread a thin layer of the meat sauce on the bottom of a 9x13 inch baking dish. Arrange half of the roasted chiles in a single layer over the sauce.

Layer and Top with Cheese: Spoon half of the remaining meat sauce over the chiles. Top with another layer of chiles, followed by the rest of the meat sauce. In a separate bowl, toss the grated Cheddar and Monterey Jack cheeses together. Sprinkle the cheese evenly over the top of the casserole. What works best for me is ensuring the cheese covers right to the edges for a lovely, crispy crust.

Bake Until Golden: Bake, uncovered, for 30-35 minutes, or until the sauce is bubbling and the cheese on top is completely melted and turning golden brown at the edges.

Rest and Serve: Remove the casserole from the oven and let it rest for at least 10 minutes before serving. This is crucial for letting it set, so it holds its shape when you serve it. Garnish with fresh coriander, if you like.