Friuli-Venezia Giulia and northern Italy generally — the trifolati technique for mushrooms is used throughout northern Italy wherever porcini are found (the Veneto, Piedmont, Tuscany). The Friulian version uses the locally-specific nepitella herb.
Trifolati (from the Friulian/Piedmontese term referring to preparation in the style of trifola — truffle) is the standard preparation for fresh porcini and other wild mushrooms in Friuli: the mushrooms are cleaned, sliced thin, and cooked rapidly in olive oil and butter with garlic and fresh nepitella (field mint, specific to the region) over high heat until golden and concentrated, then finished with a splash of white wine and fresh parsley. The high-heat, rapid technique preserves the mushroom's texture while concentrating its flavour — completely different from the slow braise or soup preparations of other regions.
Fresh porcini trifolati is one of the greatest flavour experiences available in Italian autumn cooking — the seared, golden mushroom has a meaty, nutty concentration from the Maillard reaction; the garlic and nepitella add aromatic depth; the butter richness rounds everything. The wine deglaze brightens the final result. Served on grilled bread or alongside polenta, it needs nothing else.
The mushrooms must be clean and dry — moisture causes steaming rather than searing. Slice to 3-5mm — thin enough to cook through quickly, thick enough to maintain texture. Heat a wide, heavy pan to very high heat with both butter and olive oil (butter for flavour; oil to raise the smoke point). Add the mushrooms in a single layer — do not crowd or they steam. Leave without stirring for 2 minutes until the undersides are golden, then toss. Add sliced garlic and nepitella (or thyme if unavailable) in the last minute of cooking. Deglaze with a splash of dry white wine — it should evaporate in 30 seconds. Season with salt only at the very end (salt extracts moisture and prevents browning if added early). Finish with chopped fresh parsley.
Nepitella (Calamintha nepeta) is the traditional herb for funghi trifolati in Friuli and Tuscany — its flavour is a cross between mint and oregano, and it has an affinity for mushrooms that other herbs don't replicate. Fresh thyme is the best substitute. The butter-oil combination is the key technique — pure oil produces a less rich result; pure butter burns at the required temperature.
Washing mushrooms under running water — they absorb moisture and steam rather than sear. Crowding the pan — multiple layers cause steaming; work in batches for a large quantity. Adding salt early — the moisture extracted inhibits the Maillard reaction. Cooking at too-low heat — the mushrooms stew in their released moisture rather than searing.
Giorgio Locatelli, Made in Italy; Slow Food Editore, Friuli-Venezia Giulia in Cucina