Preheat oven to 400 degrees; butter a 9-inch circle in the center of a baking sheet. In a large bowl, stir together the flour, sugar, baking powder and salt. Cut the butter into 1/2-inch cubes and distribute them over the flour mixture. With a pastry blender or two knives used scissors fashion, cut in the butter until the mixture resembles coarse crumbs. In a small bowl, stir together the eggs, orange juice, vanilla extract and orange peel. Add to the flour mixture and stir to combine. The dough will be sticky. With lightly floured hands, knead in the chocolate chips until they are evenly distributed. With lightly floured hands, pat the dough into an 8-inch circle in the center of the baking sheet. If desired, brush the egg white mixture over the tops and sides of the dough. With a serrated knife, cut the dough into 8 wedges. Bake for 20 to 25 minutes, or until a toothpick inserted into the center comes out clean. Remove the baking sheet to a wire rack and cool for 10 minutes. With a spatula, transfer the scones to a wire rack to cool. Cut into wedges if necessary. Serve warm or cool completely and store in an airtight container. These scones freeze well.