Combine all topping ingredients in a large bowl; blend with a pastry blender OR 2 knives until well mixed. Sprinkle half the mixture in bottom of well greased 12-cup (3 L) fluted tube pan. Reserve remaining topping.
Combine 2 cups flour, sugar, undissolved yeast and salt. Heat water, milk and butter until very warm (120° to 130°F/50° to 55°C). Gradually add to dry ingredients. Beat 2 minutes at medium speed of electric mixer, scraping bowl occasionally. Add eggs and 1/2 cup flour. Beat 2 minutes at high speed, scraping bowl occasionally. Stir in remaining flour and chopped chocolate to make a stiff batter.
Spoon batter over topping in pan. Sprinkle remaining topping over batter. Cover; let rise in warm, draft-free place until doubled in size, about 1 hour.
Bake at 375°F (190°C) for 30 to 35 minutes or until done. Remove from pan; let cool on wire rack.