Use a vegetable grater to grate the butter, then place it back in the refrigerator while you prepare the rest of the ingredients.
Measure the half and half, and mix the egg with it. Refrigerate until use.
Process the roasted pistachios with the sugar until fine, then transfer the mixture to a large bowl.
To the pistachio-sugar mixture add the flour, baking powder, and chopped pistachios.
Use your hand to rub the cold, grated butter into the flour mixture until you no longer notice any butter pieces. This should take about 60-90 seconds, and the mixture should look slightly moist. Pour over 1/2 cup of the half-and-half and egg mixture then use a fork to distribute the liquids and hydrate the flour. The mixture should look clumpy, and hydrated but not sticky or smooth.
Drop the mixture over a clean work surface and use your hands to press it into a rectangle dough. About 6x8-inches.
Fold the dough in half over itself and press it again into a 11x7-inches rectangle.
Use a sharp knife, or abench scraper to cut the dough at the center so you'll have two squares.
Cur each sqaure into four triangles.
Place the triangles over a large baking sheet lined with parchment apaper, and brush each with the left overs liquid mixture.
Place the pan in the refrigerator while the oven warms up to 375°F.
Bake over the middle oven rack for 25-30 minutes, until the scones are slightly puffed and medium golden brown.
Remove from the oven and allow to cool for at least 20 minutes before glazing and servng.