- Put the steak into a large, plastic, sealable bag. Reserve 1 teaspoon of the spice mix, and add the remainder to the steak, together with two teaspoons of the oil and the juice of ½ lime. Give the bag a good shake to coat the meat and leave in the fridge to marinate overnight.
- Finely slice six of the shallots and put in a bowl with the cloves and chilli flakes. Squeeze over the remaining lime juice. Cover and marinate in the fridge overnight.
- When ready to cook the next day, remove the steak and shallots from the fridge and allow both to come up to room temperature. Heat the oven to 200C/fan 180C/Gas 6.
- Heat a frying pan or griddle pan and cook the steak on each side for three to four minutes for rare-medium (or longer if you prefer it well done). Once cooked, set aside for five minutes to rest, then slice.
- While the steak is cooking, finely dice the remaining shallots. Heat the remaining oil in a saucepan and gently cook the shallots for 3-4 minutes. Tip the beans into the pan along with the reserved spice mix and heat through. When hot, remove from the heat, mash with a fork, and season to taste.
- While the steak is cooking, place the tortillas on a baking sheet and warm in the oven for 6-7 minutes until they are crisp. Remove from the oven and keep warm.
- To construct the tostadas, spread the crispy tortillas with the beans, top with the sliced steak and finish with the marinated shallots and coriander. Serve with the lime wedges on the side.
Marinating the steak overnight will maximise the flavour of the meat. Leaving the shallots to marinate in lime juice at the same time will add a zingy freshness to the finished dish.