Crumble mixture: Place pieces of broken chocolate and brown sugar in food processor or blender; process about 15 to 20 seconds or until as fine as coarse ground coffee.
Add orange rind, cinnamon, coffee, butter and pecans; process a short time until nuts are finely chopped and set aside.
Coffee Cake: Place flour, sugar, baking powder and salt in food processor; process for a few seconds to combine or prepare by hand using a pastry blender.
Sprinkle small butter cubes over dry ingredients; process only 5-6 seconds to distribute butter into very small pieces, or use pastry blender.
Transfer to a bowl, then spread mixture to form a well in the center.
Beat whole egg lightly with half and half; pour, all at once, into dry ingredients and, using a folding motion, stir to combine ingredients - mixing only until liquid is all absorbed. (Do not overmix. This should take only 15-20 hand strokes.)
Sprinkle the crumble mixture over dough in bowl; with a table knife, draw across in 2 directions to marble crumble with dough. (Do not combine thoroughly.)
Heavily grease cups of muffin pans, disposable foil pans, glass custard cups or cupcake liners; when portioning dough, mixture will be rough but will come together after baking.
To make large size muffins, fill cups level to top, yielding 9 muffins; for medium muffins, fill cups 2/3 full, yielding 12 muffins.
Prepare egg wash by mixing water with egg yolk.
Brush muffins with egg wash; bake at 325 for 15-17 minutes, depending upon the size of the muffins.
Muffins should be golden brown and baked in the center.
Cool in pans about 5 minutes to firm muffins before removing; serve warm.
I edited the baking temperature. Originally, it said 400--OMG that's too hot--so I cooled it down to 325 so the muffins wouldn't be dried out. But all ovens vary--I just think that was too hot.