To remove the need for last-minute stirring, you can serve risotto as a cake. Make the risotto in advance, taking it slightly beyond the al dente stage (about 20 minutes), then add the mascarpone, Parmesan, and tomato. Spread the mixture out in a square pan lined with wax paper, cover, and chill for 2–4 hours. When ready to serve, heat 3½ Tbsp butter in a large frying pan. Cut the risotto cake into 4 squares and quickly pan-fry for about 3 minutes on each side until golden, taking care when you flip them over. Serve immediately.