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1
Mound the semolina on a work surface and work in the lukewarm water gradually, kneading until a firm, smooth dough forms that does not stick to the hands and shows no cracks when pressed. Wrap and rest at room temperature for 30 minutes. The dough is ready when it holds its shape under a thumb press and springs back slowly.
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2
Pinch off a small piece of dough and roll it on the surface into a thin rope roughly 6 mm in diameter. Lay the ferro (knitting needle or thin iron rod) diagonally across one end of the rope and press lightly to adhere. Roll the ferro forward so the dough winds around it in a spiral; then draw the ferro back across the surface, pressing gently. The fileja springs off the ferro as a loose helix. Transfer to a semolina-dusted tray. Repeat until all dough is shaped. The pasta is ready when each piece holds its open spiral without collapsing.
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3
This is where the dish lives or dies: warm the olive oil in a wide pan over medium-low heat, add the crushed garlic clove and the nduja, and work the nduja with a spoon until it melts entirely into the oil. The fat must render fully and take on a deep red-orange colour, with the chilli perfume infusing the oil, before any tomato is added. If tomato is added too soon, the fat will not emulsify and the sauce will be greasy and flat.
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4
Add the hand-crushed San Marzano tomatoes to the nduja-infused oil and stir to combine. Add the pinch of dried Calabrian oregano. Cook uncovered over medium heat for a minimum of 10 minutes, stirring occasionally, until the tomato has reduced and concentrated around the nduja fat into a saucy, cohesive base. The sauce is ready when it pools and holds briefly at the edges of the pan rather than running thin.
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5
Bring a large pot of well-salted water to a rolling boil. Cook the fileja for 10–12 minutes; they are dense and require the full time. Taste at 10 minutes — the pasta should be cooked through with a slight resistance at the very centre.
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6
Transfer the fileja directly to the sauce with a ladle of pasta cooking water. Toss over medium heat for 1–2 minutes until the water is absorbed and the sauce clings inside the spirals of each helix. The dish is ready when no liquid pools at the base of the pan and the fileja surface carries an even red-orange coat.
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7
Divide among four warmed bowls and finish each portion with finely grated ricotta salata. Serve immediately.