How to Make It
Combine the rice, broth and ½ teaspoon salt in a medium pot. Bring to a boil. Stir once, cover, and reduce heat to low. Simmer for 18 minutes. Remove from heat and let stand, covered, for 5 minutes; fluff with a fork and let cool.
Add the sausage to a nonstick skillet and cook over medium heat, breaking up the meat as it cooks, about 5 minutes. Remove from heat and let cool slightly, then finely chop the sausage and add it to a large bowl with the cooled rice, ¾ cup Parmesan, and mozzarella. Mix thoroughly and season with salt and pepper. Stir in 2 lightly beaten eggs. Transfer the mixture to an airtight container and refrigerate for at least 4 hours.
Meanwhile, wash the skillet and return it to the stove. Add the olive oil and warm over medium heat. Add the panko and cook, stirring constantly, until the bread crumbs are toasted and golden brown, about 5 minutes. Transfer to a medium/large bowl to cool. Once cool, stir in the fine breadcrumbs and ¼ cup Parmesan. Set mixture aside.
Heat oven to 400°. Beat the remaining eggs in a medium bowl. Using a 1½-inch spring loaded scoop or two level tablespoons of the mixture, form the rice into balls, applying light pressure to keep the mixture together. Working one at a time, roll the balls in the beaten egg followed by the breadcrumb mixture. Place one ball in each cup of 1½ mini-muffin pans (about 36 cavities total). Bake until heated through and cheese has melted, 15 minutes. Serve warm.