Blend tapenade ingredients excluding mayonnaise until smooth.
Stir the mayonnaise into the tapenade mixture.
Melt butter in a saucepan and cook rice for 3 minutes over low heat.
Add wine and cook for one additional minute.
Gradually stir in warm stock until absorbed and rice is cooked.
Fold in tomatoes and spring onions, season, and let cool.
Prepare a bowl with beaten egg and a plate with flour.
Roll rice into balls, dip in egg, and coat in flour.
Heat oil in a heavy saucepan to 170°C.
Fry rice balls for 4 minutes until golden-brown and drain on paper.
Serve the arancini with the prepared tapenade.