1. Dough: In food processor, pulse sugar and tea until tea is finely ground; set aside. In large bowl, whisk together flour and bread booster; set aside. Whisk sugar mixture, yeast and salt into flour mixture; set aside.
2. In small saucepan set over low heat, cook milk and butter for 3 to 5 minutes or until milk is warm and butter is partially melted (120ºF to 130ºF/50ºC to 55ºC on instant-read thermometer).
3. In bowl of stand mixer fitted with dough hook, mix warm milk mixture, eggs, egg yolk and vanilla. Mix in flour mixture on medium speed, scraping down side of bowl occasionally, for 2 to 3 minutes or until ball of dough starts to form and pull away from side of bowl.
4. Transfer dough to lightly floured work surface; knead until smooth and elastic, and dough springs back when lightly pressed with 2 fingers, about 6 to 8 minutes. Cover with tea towel; let stand for 10 minutes.
5. Filling: In heatproof bowl set over saucepan of simmering water, melt chocolate and butter, stirring for about 10 minutes or until smooth. Remove from heat. Stir in granulated sugar, icing sugar, cocoa powder and salt. Let cool to room temperature.
6. Assembly: Line two 8 1/2 x 4 1/2-inch (21 to 11 cm) loaf pans with parchment paper; set aside.
7. Divide dough in half. On lightly floured work surface, working with one portion of dough at a time, roll out into 15- x 11-inch (38 x 28 cm) rectangle. Spread with half of the chocolate filling, leaving 1-inch (2.5 cm) border. Sprinkle half of the walnuts over top. In small bowl, whisk egg with milk; brush over bottom edge of one long end. Set remaining egg wash aside.
8. Starting from long end (not brushed with egg wash), roll up tightly into log. Pinch ends to seal seams. Roll log back and forth on work surface into 18-inch (46 cm) log of uniform thickness. Repeat with remaining dough.
9. Cut each 18-inch (46 cm) log in half crosswise. Using sharp knife, slice each half log lengthwise to make 4 pieces, revealing the filling. With cut sides facing up, pinch 4 ends together. Twist and braid the 4 pieces of each log together, keeping cut sides facing up, to form two loaves.
10. Transfer each loaf to prepared pan. Cover and let rise for 45 to 60 minutes or until doubled in size.
11. Preheat oven to 350?F (180?C). Brush remaining egg wash over top of each loaf. Bake for 45 to 65 minutes or until golden brown and instant-read thermometer inserted into centre of loaf registers 190?F (88?C). (If bread is browning too quickly, tent loosely with foil halfway through cooking time.) Let cool in pan on rack for 15 minutes. Turn out loaves onto rack; let cool completely.
12. Glaze: Meanwhile, in small saucepan set over low heat, bring corn syrup, 2 tbsp (30 mL) water and tea to boil. Remove from heat; let steep for 10 minutes. Strain, discarding tea.
13. In heatproof bowl set over saucepan of barely simmering water, melt chocolate and butter until smooth. Stir in corn syrup mixture; let cool to room temperature. Drizzle glaze over loaves. Let stand for about 45 minutes or until glaze is set.

Tip: Substitute pecans, hazelnuts or almonds for walnuts if desired.