Grease a 9x13 pan.
Chop bacon into 1 ½ inch pieces. Cook until crispy. Set aside on paper towels and pat to remove excess grease. Pour all but a couple of tablespoons of the bacon grease out of the pan. Cook shallots in remaining fat until softened. Set aside.
Whisk eggs for 1–2 minutes. Whisk in milk, mustard, salt, and pepper. Stir in reserved bacon, shallots, cheese, and parsley. Fold in the torn bread.
Pour into the prepared pan and cover with foil. Refrigerate for at least 6 hours, up to 24.
Preheat oven to 350ºF. Bake strata for 1 hour and 10 minutes, or until golden, puffed, and set in the center. Remove from oven and let rest for 5 minutes before serving.
