Preheat oven to 350 degrees F. Place 1 1/4 cups walnuts on a baking sheet. Bake for 7 to 9 minutes or until toasted. Coarsely chop 1 cup of the walnuts. Finely grind remaining walnuts; set aside. Increase oven temperature to 375 degrees F.
In a large bowl combine flour, finely ground walnuts, baking powder, baking soda, and salt. Using a pastry blender, cut in butter until the mixture resembles coarse meal. Stir in the 4 ounces Gruyere, 1 cup coarsely chopped walnuts, and thyme. Make a well in center of mixture. In a small bowl combine egg, buttermilk, honey, and mustard; add ll at once to flour mixture. Using a fork, stir just until moistened.
Turn dough out onto a lightly floured surface. Knead dough by folding and gently pressing it for 10 to 12 strokes or until nearly smooth. Divide in half. Pat or lightly roll each half to a 3/4-inch thick circle, about 6 inches in diameter. Cut each circle in 8 triangles. Place triangles 2 inches apart on greased or parchment-lined baking sheet. Bake for 18 to 20 minutes or until golden brown.
Transfer to cooling rack. If desired, top with additional cheese, walnuts, and thyme. Serve warm.