For the topping, start by making the brown butter. Add 2 ounces butter (1/2 stick) and place it in a saucepan and cook for 2-3 minutes, until butter has bubbled, crackled and turned a very, VERY dark - near black - hue. Remove from heat and set aside to cool. In a medium bowl, combine the cold butter, flour, walnuts, brown sugar, salt, cinnamon and nutmeg in a medium bowl. Rub the mixture with your hands until the butter is broken up into bits, resembling the size of peas. Pour in the cooled brown butter and mix until thoroughly distributed. Sprinkle the topping mixture atop the filling mixture. Transfer the baking dish to the oven and bake for 35 to 40 minutes, until the top is a light golden brown and the juices from the peaches are bubbling. Serve warm or room temperature; and definitely with a scoop of ice cream or whipped cream.