Preheat the oven to 350 degrees F. In a 8 x 8-inch baking dish (or something equivalent), add the pears, apples, white sugar, brown sugar, all-purpose flour, minced fresh ginger, vanilla extract and salt. Toss until pears are thoroughly coated. Set aside.
To a medium bowl, whisk together the all-purpose flour, brown sugar, oat flakes and chopped walnuts.
In a small saucepan, set over medium-high heat, add the cubed butter. Brown the butter until it goes from yellow and bubbling to a very, very dark brown color. It might appear burnt and it is, but not to worry, it'll taste delicious. Pour the burnt butter into the medium bowl that's holding the flour and oat mixture. Using a spoon, mix the mixture until clumpy and everything is coated in butter. Pour the crumble atop the filling and spread it out evenly. Transfer it to the oven to bake for 35 to 40 minutes, until the crumble is bubbling and the top is golden brown.
I'm not a super bossy person, but you must, you MUST eat this crumble warm with a scoop of cold vanilla ice cream.