Place steak chunks in a bowl.
Drizzle olive oil over steak and onions. Toss to coat.
In a bowl combine the brown sugar, garlic, thyme, rosemary, 1 teaspoon salt and pepper. Sprinkle over the steak and toss to coat well.
Prepare a grill fire to 350°.
Cook the steak chunks and onion over indirect fire with the grill closed for 5 minutes.
Turn the steak and onions and continue to cook another 7 - 10 minutes until steak reaches 140°.
Remove from grill. Cool 10 minutes. Dice the steak and onions and set aside.
Alternately, cook the steak and onions in a dutch oven or large pan with 2 tablespoons of olive oil over medium-high heat, until seared on all sides, about 15 minutes.
Meanwhile, cook the bacon in a dutch oven or deep pan until crisp. Remove bacon to a paper towel lined plate and set aside.
Cook the carrots and celery in the bacon drippings over medium for 3 minutes, stirring occasionally. Add the mushrooms and continue to cook until vegetables are softened.
Remove vegetables and set aside.
Add additional bacon drippings or olive oil to the pan with the all purpose flour. Season with 1 teaspoon salt and whisk continually about 3- 4 minutes until flour starts to brown.
Pour in Guinness Stout and whisk until combined.
Whisk in the beef broth and bring the mixture to a boil.
Add diced potatoes to the gravy and cook for about 5 minutes.
Stir in the reserved vegetables.
Next add in the steak and onions.
Grate the chocolate into the filling.
Crumble the bacon and add to the pan, stirring until well combined.
Remove from heat.
Spoon the filling into 2 9- inch pie plates.
Roll the puff pastry out on a lightly floured board.
Place over the filling and trim the edges.
Make a few slits with a sharp knife to vent the filling.
Beat the egg with a tablespoon of water and brush over the puff pastry.
Bake the pies for 45 minutes to 1 hour.
Remove from oven and allow to rest about 10 minutes before serving.