Blend dry ingredients together in a large bowl. Cut in cold butter using a pastry blender until the butter is well distributed, but some crumbles remain. Using a fork, blend in the buttermilk until a tacky dough forms. Pour out the dough on a lightly floured board and gently push dough into a rectangle about 1“ thick.
Scatter dates and walnuts on top of the rectangle. Fold over a few times. Pat back into shape and allow dough to rest for ½ hour on the board, then ½ hour refrigerated.
Cut dough into circles, squares or triangles depending on your preferred biscuit shape. Brush tops of biscuits with egg wash. Place biscuits on a parchment covered cookie sheet. Bake in a preheated 450° oven for 12 minutes.