In a bowl, mix 2 3/4 cups flour, semolina flour, 3/4 cup sugar, pistachios, baking powder, and salt.
Cut 1/2 cup butter into chunks and add to bowl. With your fingers or a pastry blender, rub or cut in butter until mixture forms coarse crumbs.
Add 1 1/3 cups milk and the lemon peel to flour mixture and stir with a fork just until evenly moistened.
Scrape onto a floured board and, with lightly floured hands, knead just until dough comes together (it will be sticky). Divide in half and form each half into a ball. Pat each ball into a 7-inch round about 1 inch thick. Cut each round into six equal wedges.
Place wedges 2 inches apart on a buttered 14- by 17-inch baking sheet. Beat egg yolk with remaining 2 tablespoons milk just to blend. Brush tops of wedges with egg mixture and sprinkle lightly with sugar.
Bake on the middle rack in a 375° regular or 350° convection oven until scones are richly browned, about 25 minutes. Serve warm.
Nutritional analysis per scone.