Dry Out Bead– Preheat oven to 300F. Tear sourdough bread into chunks a little larger than the size of a quarter. Add torn bread to a baking sheet and bake for 30 minutes, tossing half way through.

Crisp Prosciutto– Turn oven heat up to 400F. Place prosciutto slices on an oven safe wire baking rack about an inch apart from each other & bake for 10 minutes until crisp. Allow prosciutto to cool completely, then crumble.

Prepare Vegetables– Melt butter in frying pan over medium heat. Add diced onion to pan and sauté for 4 minutes. Add minced garlic and fresh spinach to pan. Cook and stir until spinach has wilted.

Combine & Chill– In a small bowl whisk together mustard, eggs, milk, salt, and pepper. In a large bowl combine dried bread, vegetable mixture, crispy prosciutto, and 3/4 cup Parmesan. Pour milk & egg mixture over everything, toss to combine. Add everything to a 9 inch baking dish, cover with plastic wrap, and place in the refrigerator for at least 1 hour (but up to 18).

Bake– When ready to cook, preheat oven to 375F. Remove plastic wrap and top strata with remaining Parmesan cheese. Bake 25-30 minutes uncovered. Remove from oven, cover with aluminum foil, and continue baking 35-40 minutes