Boil the potatoes until soft.
Mash with a knob of butter and a splash of milk.
Add wasabi paste to taste. Keep warm.LIME CREAM SAUCE
Cook the cornflour and butter over low heat until smooth.
Slowly add a little water and stir until the sauce thickens.
Add the lime rind and juice and cook until the sauce thickens.
Remove from the heat and let it cool completely.
Add the cream and whisk until smooth.TUNA FILLETS
Brush the tuna fillets with olive oil and sear on all sides in a smoking hot griddle pan (it must still be pink inside).
Serve the seared tuna on top of the wasabi mash, drizzled with lime cream sauce.
NOTE: Make sure the sauce is cool before adding the cream or it might curdle.