Choose a sliced-fruit mostarda, not a whole-fruit mostarda, for the topping.

Warm the olive oil and 1 tablespoon butter in a large saucepan over moderate heat. Add the onion and saute until soft, 5 to 8 minutes. Add the squash, a pinch of salt and 1/2 cup hot broth. Cover and simmer gently until the squash is almost tender, about 8 minutes. Stir in the rice.

Begin adding the remaining hot broth 1/2 cup at a time, stirring occasionally and adding more broth only when the previous addition has been absorbed. It should take 18 to 20 minutes for the rice to become al dente, firm but not chalky. You may not need all the broth. If you need more liquid, use boiling water. The risotto should be creamy, neither soupy nor stiff.

Cover, remove from the heat, and let stand for about 2 minutes to complete the cooking. Stir in the remaining 2 tablespoons butter and the cheese. Taste for salt and add several grinds of black pepper. Divide among 4 to 6 bowls and top each serving with a spoonful of mostarda. Serve hot.

Photo by wlayton