In a medium bowl, whisk together flour, walnuts, sugar, salt, cinnamon, and cardamom.
In a small saucepan, melt butter over medium-high heat. Cook, stirring often, until the milk solids in the butter turn a light brown color and the butter smells nutty and fragrant, 4 to 5 minutes. Pour over the flour mixture, stirring to combine. (The mixture should be crumbly.) Refrigerate for at least 15 minutes or until ready to use
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/apple-butter-pie/