Heat butter in a medium saucepan over medium heat; cook onion and garlic, stirring, for 2 minutes or until onion is softened. Add rice, stir to coat in mixture.
Add wine to pan; cook, stirring, for 2 minutes or until wine has evaporated. Gradually add hot stock, 1 cup at a time, stirring continuously, for 25 minutes or until all stock is used and the rice is just cooked. Add cream; cook, stirring, a further 2 minutes.
Remove pan from heat, stir in cheeses. Cool for 20 minutes, then add egg yolks; season. Spread rice mixture over a baking-paper-lined oven tray; cool for 15 minutes or until cool enough to handle.
Divide risotto into slightly rounded tablespoons of mixture. With wet hands, roll rice mixture into balls, then in breadcrumbs to coat. (The mixture will be quite delicate.)
Fill a large saucepan one-third full with oil; heat to 180°C/350°F (or until a cube of bread turns golden in 10 seconds). Fry risotto balls, in batches, 2 minutes, turning occasionally, or until browned and heated through. Drain on paper towel. Serve immediately with lemon wedges.