Warm the stock in a saucepan over low heat and keep it at a bare simmer next to the stove.

Pat the perch fillets dry with paper towel, season with salt and pepper, then dust lightly in flour, shaking off the excess.

Melt 30 g of the butter in a 28 cm / 11-inch heavy-bottomed saucepan over medium heat. Add the shallot and cook for 3 to 4 minutes until soft and translucent, not browned.

Add the rice and toast for 2 minutes, stirring, until the grains look glassy at the edges.

Pour in the wine and stir until fully absorbed, about 1 minute.

Add the warm stock one ladle at a time, stirring often, waiting for each ladle to be absorbed before adding the next. This takes 16 to 18 minutes; the rice should have a firm, not chalky, center when it's ready.

While the risotto cooks, melt the remaining 60 g butter in a 26 cm / 10-inch skillet over medium-high heat. Add the sage leaves and fry for 30 seconds until crisp and fragrant, then lift out onto a paper towel.

Add the floured perch fillets to the same skillet. Fry for 2 to 3 minutes per side until golden and the internal temperature reaches 63 C / 145 F, the flesh opaque and flaking easily with a fork.

Squeeze the lemon juice over the fillets and take the skillet off the heat.

Off the heat, stir the remaining 30 g butter into the risotto (mantecatura) until glossy and loose. Season with salt and white pepper.

Spoon the risotto onto warm plates, top each portion with a perch fillet, and scatter the fried sage leaves and lemon zest over the top.