Scald the milk and let it cool to 110 degrees F. Add 1/4 cup of the sugar and the yeast and let stand until foamy, about 10 minutes.
Combine the orange zest with the remaining sugar in a food processor and process until zest is finely ground.
In a heavy-duty electric mixer, combine the yeast mixture, zest and sugar mixture, eggs and egg yolks. Beat until combined, about 30 seconds. In a separate bowl, sift together the flour and salt. Gradually add the dry ingredients to the liquid in the mixer bowl, beating constantly until the dough is sticky and soft.
Add 2 sticks (1 cup) of butter, 1 tablespoon at a time, beating constantly until combined. Beat an additional 30 seconds.
Coat a large bowl with remaining tablespoon butter. Turn the dough out onto a lightly floured board; form a ball WITHOUT KNEADING and place in the bowl, turning to coat the dough with butter. Cover with plastic wrap and a towel and set aside to rise in a warm place until doubled in bulk, about 1 to 1-1/2 hours.
Turn the dough out onto a lightly floured board. Punch down to remove air bubbles and return to the bowl. Cover with plastic wrap and refrigerate a minimum of 6 hours, or overnight.
Turn the dough out onto a lightly floured board and gently knead in the chocolate pieces. Divide the dough into 16 equal parts. Roll each between your hands to form a 1-1/2" round cylinder. To make the traditional brioche topknot, lay the cylinders on a counter and roll the side of your hand back and forth at a point about an inch from the top, so you form a shape like a bowling pin. Place the dough in buttered brioche tins or muffin cups, pinched side up, and gently press the tops down toward the bottom of the tim.
Place the tins on a baking sheet, cover with plastic wrap and a towel and set aside in a warm place to rise until doubled, about 1-1/2 hours. Preheat oven to 375 degrees F.
Bake for 20 minutes. While the brioches are baking, make the glaze. ORANGE GLAZE: Whisk the ingredients together to form a paste and spoon about 1 tablespoon over each warm brioche.