Individual Broccoli And Cauliflower Cheddar Gratins

Ingredients

• kosher salt
• 4 cup cauliflower florets
• 4 cup broccoli florets
• 1½ tablespoon unsalted butter
• 1½ tablespoon all-purpose flour
• 1½ cup whole milk
• 1½ cup grated sharp white cheddar cheese
• 1½ teaspoon grated lemon zest
• ¾ teaspoon dijon mustard
• pinch of cayenne pepper
• 2 tablespoon toasted bread crumbs (see notes below)