For the tuna:
2 150g tuna steaks
2 tbsp dark soy sauce
1 tbsp mirin
1 garlic clove, crushed
1 tbsp black sesame seeds
1 tbsp white sesame seeds
1 tsp sushi ginger
sesame oil, for frying
For the wasabi mash:
approx 500 g floury potatoes
150 ml warmed milk
knob of butter
1 tsp sea salt
1 tsp wasabi paste (or to taste)