Heat oven to 350 F.

To make walnut crisp topping: In food processor, pulse 1 cup walnuts until finely ground. Set aside in separate bowl. In food processor, pulse remaining 1/2 cup walnuts until chopped. Set aside.

In medium bowl, combine ground walnuts, flour, brown sugar, oats and cinnamon. Cut butter into mixture until coarse crumb forms.

To make apple pear filling: In large bowl, toss apples, pears, sugar, cornstarch, cinnamon, salt and lemon juice.

Pour fruit mixture in bottom of 12-inch cast-iron pan.

Layer walnut crisp topping mixture over fruit.

Bake 45 minutes, or until fruit mixture is hot and bubbly and topping is golden brown.

Top with ice cream and caramel sauce, if desired.