Ingredients:

  • cups stale French bread, sourdough, or challah (cubed 1-inch)
  • cup cooked breakfast sausage or crumbled bacon
  • /2 cup diced yellow onion
  • /2 cup chopped fresh spinach
  • 1/2 cups sharp, shredded Cheddar cheese
  • large eggs
  • cups whole milk
  • /2 cup heavy cream
  • teaspoon Dijon mustard
  • teaspoon dried English mustard powder
  • teaspoon dried thyme
  • teaspoon kosher salt
  • /2 teaspoon freshly ground black pepper
  • /2 cup grated Gruyère or Monterey Jack cheese
  • tablespoons chopped fresh chives or parsley (for serving)

Instructions:

  1. Preheat oven to 375°F (190°C). Grease a 9x13 inch baking dish thoroughly.
  2. Lightly sauté the diced onion in a splash of oil or butter until softened (about 5 minutes). If using raw sausage, cook and drain it now.
  3. Spread half of the cubed bread evenly into the prepared baking dish.
  4. Scatter the cooked meat, sautéed onions, spinach, and the 1 1/2 cups of Cheddar cheese evenly over the bread layer.
  5. Cover the fillings with the remaining half of the bread cubes.
  6. In a large mixing bowl, whisk together the eggs, milk, heavy cream, Dijon mustard, mustard powder, thyme, salt, and pepper until thoroughly combined and slightly frothy.
  7. Slowly and evenly pour the entire custard mixture over the bread and fillings in the baking dish, gently pressing down the top layer to ensure all the bread absorbs the liquid.
  8. Cover the dish with cling film and refrigerate for a minimum of 30 minutes, ideally 2-4 hours, or even overnight, allowing the bread to fully soak.
  9. Remove the casserole from the fridge 30 minutes before baking. Sprinkle the top evenly with the Gruyère/Jack cheese.
  10. Bake for 45–55 minutes, or until the top is golden brown, puffed, and a knife inserted near the centre comes out mostly clean (custard should be set).
  11. Let the casserole rest on a wire rack for 10 minutes before slicing. Garnish with fresh chives before serving.