For the tagliatelle, half-fill a deep-based pan with the vegetable oil and heat until a cube of bread dropped in sizzles and turns golden-brown in 30 seconds. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Deep-fry the pasta in the oil for 3-4 minutes, or until golden-brown and crisp. Remove with a slotted spoon and drain on kitchen paper, then sprinkling over some cocoa powder and icing sugar.
For the passata, place the tomato into a food processor and blend until smooth. Season, to taste, with salt and freshly ground black pepper.
Serve the deep-fried tagliatelle with the passata spooned alongside.