cremini leek bread pudding

6 cups (1/2-inch-diced) bread cubes from a rustic country loaf, crusts removed
2 tbsp evoo 
1 tbsp unsalted butter
2 oz pancetta, diced
4 cups sliced leeks, white and light green parts (2 leeks)
1 1/2 lbs cremini mushrooms, sliced
1 tsp tarragon 
1/4 cup cooking sherry
salt & pepper
1/3 cup minced parsley
4 eggs
1 1/2 cups heavy cream
1 cup chicken stock
1 1/2 cups grated gruyere cheese, divided

1. preheat the oven to 350F. spread the bread cubes on a sheet pan and bake for 15 to 20 minutes, until lightly browned. set aside.
   
2. meanwhile, heat the oil and butter in a large saute pot over medium heat. add the pancetta and cook for 5 minutes, until starting to brown. stir in the leeks and cook 10 minutes, until the leeks are tender. stir in the mushrooms, tarragon, sherry, 1 tbsp salt and 11/2 tsp pepper and cook for 10 minutes, until most of the liquid evaporates, stirring occasionally. off the heat, stir in the parsley.
   
3. in a large mixing bowl, whisk together the eggs, cream, chicken stock and 1 cup of the gruyere. 
4. add the bread cubes and and the egg mixture to the pot with the mushroom mixture, stirring well to combine. set aside at room temperature for 30 minutes to allow the bread to absorb the liquid. pour into a baking dish (13 x 9 x 2 inches). sprinkle with the remaining 1/2 cup gruyere and bake for 45 minutes, until the top is browned and the custard is set.