Sauté the Base Vegetables: Heat the olive oil in a large, heavy-bottomed pot or Dutch oven over a medium heat. Add the chopped onion, carrots, and celery. Cook gently for 8-10 minutes, stirring occasionally, until the vegetables are soft and the onion is translucent. Don't rush this step; it builds the first layer of flavour.

Add the Pepper and Garlic: Add the chopped red pepper and continue to cook for another 5 minutes until it has softened. Then, stir in the crushed garlic and cook for one minute more, until you can smell its aroma.

Bloom the Spices: Add the ground cumin, smoked paprika, ground coriander, and chilli powder to the pot. Stir continuously for 60 seconds. What works best for me is to really get them sizzling in the oil; this toasting process, often called blooming, releases their essential oils and makes their flavour much more intense.

Add the Pastes and Tomatoes: Stir in the tomato purée and chipotle paste (if using) and cook for another minute. Pour in the two tins of chopped tomatoes and the vegetable stock. Use the stock to swill out any remaining tomato from the tins. Give everything a good stir to combine.

Simmer to Perfection: Bring the mixture to a gentle boil, then reduce the heat to low, cover with a lid, and let it simmer for at least 30 minutes. This allows the flavours to meld together. The longer you can let it simmer (up to an hour), the richer the flavour will be.

Add the Beans and Finish: Remove the lid and stir in the drained kidney beans, black beans, and cannellini beans. Add the piece of dark chocolate. Continue to simmer, uncovered, for another 10-15 minutes, allowing the sauce to thicken slightly.

Season and Serve: Turn off the heat. Season generously with salt and pepper to your taste. Finally, squeeze in the juice of half a lime – this brightens everything up wonderfully. Serve hot with your favourite toppings.