Heat oil in a saucepan over low heat, add onion, stir occasionally until tender (3-5 minutes), add rice, stir to coat, then add stock, little by little, until rice is slightly overcooked and stock is absorbed (18 -20 minutes). Add thyme and butter and stir until creamy (1-2 minutes), remove from heat. Meanwhile, finely grate 15 g provolone, add to rice mixture, spread over a tray and cool to room temperature, then refrigerate to chill (1-1½ hours).