Place a large skillet over medium heat without any oil — prosciutto contains sufficient fat to render and crisp in a dry pan. Lay the prosciutto slices in a single layer without overlapping — any overlap produces steaming between the slices rather than the crisp, rendered result the recipe requires. Cook for 2–3 minutes, turning once at the midpoint, until the fat has visibly rendered and the slices have darkened and crisped at their edges. The prosciutto will continue crisping on residual heat after being removed from the pan — pull it slightly before it appears completely done. Transfer to a paper towel-lined plate to absorb the rendered fat. Add a few grinds of black pepper over the warm prosciutto if desired. As the prosciutto cools on the plate it will develop maximum crispness — this is the correct result. Set aside and use the same skillet for the brown butter step.

Bring a large pot of generously salted water to a full rolling boil. Add the 500g of shelf-stable potato gnocchi and stir once immediately to prevent the pieces from sticking together on the pot floor. Cook until the gnocchi float to the surface, then continue cooking for 60 additional seconds — floating indicates the internal temperature has risen enough for the potato starch to expand, but the extra 60 seconds ensures the centres are heated thoroughly. Before draining, reserve 180ml of the starchy gnocchi water — this water is the emulsifying agent that converts the browned butter from a fat coating into a glossy, cohesive sauce that clings to each piece. Drain immediately and set aside.

This step requires full, uninterrupted attention — brown butter moves from perfect to burnt in under 30 seconds at the correct temperature and cannot be saved once overcooked. Wipe the skillet clean of any prosciutto residue and return it to medium heat. Add the 90g of unsalted butter and the 2 smashed garlic cloves. A light-coloured or stainless steel skillet is specifically useful here — the colour of the butter's developing milk solids is the primary visual indicator of doneness, and a dark-coloured non-stick surface obscures this colour change. Allow the butter to melt, foam, and then continue heating beyond the foam stage. The foam represents the water in the butter evaporating and the milk solids beginning to separate — allow it. Add the 12 fresh sage leaves when the butter is foaming and fragrant. The sage leaves will sizzle immediately and begin crisping. The butter's colour beneath the foam will begin shifting during the next 3–5 minutes through pale gold to a deeper golden-amber as the milk solids toast against the pan surface — it is the milk solids' toasting that produces the specific nutty, slightly caramelised complexity of true brown butter. Swirl the pan frequently rather than stirring — swirling moves the butter continuously and prevents the milk solids from sitting stationary long enough to burn. The correct moment to pull the pan off the heat is when the butter is visibly deep golden, the milk solids visible at the bottom of the pan are amber-coloured, and the aroma shifts to a specifically nutty, toasted-hazelnut character. Remove the smashed garlic cloves once they are fragrant and lightly golden — they have contributed their aromatic depth and should not remain in the sauce.

Immediately add the drained gnocchi to the pan with the browned butter and fried sage — immediately, because every second off the heat after reaching the correct brown butter colour is a second closer to burning. Toss to coat all surfaces in the browned butter. Allow the gnocchi to sit briefly in the pan — 20–30 seconds between each toss — so some pieces develop light golden contact marks against the hot pan surface. These crisped edges provide the textural contrast between the slightly crunchy exterior and the pillowy interior that distinguishes properly pan-finished gnocchi from simply warmed gnocchi. Add 60ml of the reserved gnocchi water to the pan and toss vigorously — the starchy water and the browned butter combine immediately under the mechanical action of tossing into a partially emulsified, glossy coating. The transformation is visible within 30 seconds: the separated fat and water become a cohesive, slightly thick sauce that coats each piece. Continue tossing for 1–2 minutes, adding more gnocchi water in 30ml increments if the sauce looks tight or greasy rather than glossy and flowing.

Remove the skillet from the heat completely. Add the lemon zest and the 60g of finely grated Parmigiano-Reggiano simultaneously. Toss quickly — the cheese must be added off heat to melt smoothly into the sauce rather than seizing and clumping, as it would at direct high heat. The Parmigiano's fat and protein combine with the starchy, emulsified brown butter sauce to produce a final, unified glossy coating. Crumble the crispy prosciutto over the gnocchi and fold gently to distribute — the prosciutto's salty crunch is the contrasting element that makes each forkful more interesting than the sauce alone. Scatter the toasted hazelnuts over the finished dish if using — their earthy, slightly bitter nuttiness mirrors and amplifies the brown butter's toasted hazelnut character. Finish with a pinch of flaky sea salt and a confident crack of fresh black pepper. Serve immediately — gnocchi loses its crisped edges within minutes of resting and the dish is at its best in the first 2–3 minutes after leaving the pan.