All the Magic of a Croque Monsieur, Baked in One Dish
The croque monsieur is, in my opinion, the most perfect sandwich France ever produced — buttery bread, ham, Gruyère, and that glorious blanket of béchamel, grilled until it bubbles. It is also, on a busy morning, a fair amount of fuss. This breakfast casserole keeps every bit of the magic and ditches the fuss. Layers of brioche, deli ham and nutty Gruyère, soaked in an egg custard, baked under a golden béchamel until the whole thing puffs like a savoury soufflé. The first time I served it, someone at the table said, quite seriously, “I would like this at my wedding.” I understood.
What makes it work is the overnight soak. The bread drinks up the egg mixture while you sleep, so by morning the layers have fused into something custardy and rich, and the béchamel on top goes deeply golden in the oven. It feeds a crowd from a single dish, it reheats like a dream, and it makes a weekend morning feel like a small Parisian holiday.
Why You’ll Love This Recipe
- Overnight ease. Assemble the night before, pour over the béchamel in the morning, bake.
- Feeds a crowd. One 9×13 dish serves eight to ten — ideal for holidays and houseguests.
- Pure Parisian drama. The cheese pull on this thing should be illegal.
- Infinitely riffable. Swap the ham for turkey, add mushrooms, try Comté instead of Gruyère.
- Leftovers that people fight over. It reheats in the oven better than most things do fresh.
Ingredients
Serves 8 to 10
For the casserole:
- 1 loaf brioche or thick white bread (about 500g), cut into 2cm cubes
- 300g good deli ham, torn into pieces
- 250g Gruyère cheese, shredded, divided
- 6 large eggs
- 500ml whole milk
- 2 teaspoons Dijon mustard
- Half a teaspoon freshly grated nutmeg
- 1 teaspoon fine sea salt
- Half a teaspoon black pepper
- Butter, for greasing
For the béchamel:
- 40g butter
- 40g plain flour
- 500ml whole milk, warmed
- A pinch of nutmeg, salt and white pepper
Instructions
- Step 1 — Prep the dish. Butter a 9×13-inch baking dish generously.
- Step 2 — Layer the base. Scatter half the bread cubes in the dish, then layer over the ham and half the Gruyère. Repeat with the remaining bread, ham and half of the remaining Gruyère (reserve some for the top).
- Step 3 — Make the custard. Whisk the eggs, milk, Dijon, nutmeg, salt and pepper together until completely smooth.
- Step 4 — Soak overnight. Pour the custard evenly over the layers, pressing gently so the bread absorbs it. Cover and refrigerate at least 4 hours, ideally overnight.
- Step 5 — Make the béchamel. Melt the butter in a saucepan, whisk in the flour and cook for 2 minutes. Gradually whisk in the warm milk until smooth, then simmer gently for 5 minutes until thick enough to coat a spoon. Season with nutmeg, salt and white pepper.
- Step 6 — Assemble. The next morning, spread the warm béchamel over the soaked casserole and scatter the reserved Gruyère on top.
- Step 7 — Bake. Bake at 180C (160C fan) for 45 to 55 minutes, until puffed, deeply golden and bubbling at the edges.
- Step 8 — Rest and serve. Let it stand 10 minutes before cutting — it sets as it rests and slices far more cleanly.
Tips for Success
- Day-old bread is better than fresh — it absorbs the custard without turning to mush.
- Warm the milk before adding it to the roux; cold milk is the number one cause of lumpy béchamel.
- Do not skip the rest. Cutting too early gives you a delicious but sloppy pile; ten minutes gives you clean, proud slices.
- Gruyère is worth it here — its nutty depth is the soul of a croque. Pre-shredded works, but block-and-grate melts better.
- If the top browns too fast, tent loosely with foil for the last 15 minutes.
Serving Ideas
- With a simple green salad dressed in sharp vinaigrette to cut the richness.
- Alongside fresh fruit and good coffee for a proper brunch spread.
- With roasted tomatoes on the side — their acidity loves the creamy casserole.
- For Christmas morning, when you want something spectacular with zero morning effort.
FAQs
Can I assemble it the morning of?
Yes, with a minimum 1-hour soak, but overnight is genuinely better — the texture is noticeably more custardy.
What bread works best?
Brioche is the dream, but any sturdy white bread, challah or even croissants work beautifully.
Can I make it vegetarian?
Swap the ham for sautéed mushrooms and spinach — it is just as good, honestly.
How do I reheat leftovers?
Cover with foil and warm in a 170C oven for 15 to 20 minutes. The microwave works but softens the top.
Can I freeze it?
Baked and cooled, it freezes well for up to 2 months. Thaw overnight in the fridge and reheat covered in the oven.
