Heat the oven to 350°F. Lightly grease a deep 7x11 inch baking dish.
In a medium bowl, stir all topping ingredients EXCEPT for butter together. Cut in cold butter until crumbs form (use clean hands, a pastry cutter doesn't work as well due to the nuts). Set aside in the fridge.
Combine all ingredients for the filling in a large mixing bowl, stirring well to evenly distribute the sugar and flour.
Place the filling in the prepared baking dish. Evenly cover the fruit filling with the chilled topping.
Bake the crisp for 35-40 minutes in the preheated oven, or until the topping is golden and the filling is bubbly. Rest on a rack on the counter for 10-15 minutes before serving.
Don't skip chilling the topping: This helps the topping to turn out crumbly and stay on top of the fruit - otherwise the butter could melt too fast and you'd be left with a greasy filling and a try topping.Peeling the fruit: If you want to peel the apples and pears for the crisp, feel free to do so. I actually like the pop of color the skin adds, and it helps the softer pears to stay in shape.Make ahead instructions: This is a great dessert to make ahead up to 2 days. Finish baking, then cool it completely on a rack. Cover tightly with plastic wrap and chill. To reheat, unwrap and place it in the oven at 300°F until hot. Cover the top with aluminum foil if needed to prevent too much browning.