Cook the sliced leeks, butter, and tarragon in a large shallow pan over gentle heat for 15 minutes.
Stir in the rice until coated in butter and add the white wine.
Simmer until the wine has evaporated.
Add the hot stock gradually, a ladleful at a time, stirring frequently until absorbed.
Continue cooking for 20 minutes until rice is creamy but firm, then season with salt and pepper.
Place spoonfuls of grated parmesan into a non-stick pan over low heat and flatten into rounds.
Flip the crisps once the bottom is golden and cook for another minute.
Serve the risotto in bowls topped with the parmesan crisps.