1/4 pound (1 stick) unsalted butter at room temperature
8 ounces Stilton cheese, crumbled (about 12 ounces with rind), at room temperature
1 1/2 cups all-purpose flour
2 teaspoons kosher salt
1 teaspoon freshly ground black pepper
1 extra-large egg beaten with 1 tablespoon water for egg wash
1/2 cup roughly chopped walnuts