Brussels Sprouts Gratin with Caramelized Shallots

INGREDIENTS

• 3 cups coarse fresh bread crumbs
• 3 Tbs. unsalted butter, melted
• 1 1/2 tsp. lemon zest
• 1/2 tsp. kosher salt
• 1/2 tsp. freshly ground pepper
• 2 Tbs. minced fresh flat-leaf parsley
• 1 Tbs. unsalted butter
• Kosher salt, to taste, plus 2 tsp.
• 2 lb. brussels sprouts, trimmed and halved lengthwise
• 2 Tbs. all-purpose flour
• 8 oz. Gruyère cheese, grated
• 1/2 oz. Parmigiano-Reggiano cheese, grated
• 1 tsp. lemon zest
• 3/4 tsp. freshly ground pepper
• 1 cup heavy cream
• 1 jar (8 oz.) caramelized shallots, liquid strained off