Whisk all ingredients in a metal bowl until smooth.
Strain through a fine sieve, transfer to a 1L siphon, charge with 2 siphon cartridges, and refrigerate for at least 4 hours.
In a pot, heat butter and olive oil.
Add shallots, spring onion & leek- sauté for 4 minutes.
Add mushrooms and cook until dry.
Deglaze with sweet red wine & reduce by 90%.
Stir in truffle paste, mix well, and let cool.
Heat sunflower oil to 180°C (356°F).
Place a small spoon in the hot oil, drain, and press the siphon trigger to add a little beignet mixture.
Add a small amount of mushroom duxelles, cover with more mixture, then dip the spoon into the oil.
Fry on both sides until golden brown.
