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Ingredients
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Sandwich
Mornay sauce (béchamel with cheese)
Eggs
Finishing / optional
Method
Mornay sauce (béchamel with cheese)
- 1
Make roux
In a medium saucepan over medium heat, melt 3 tbs unsalted butter. Once foaming and bubbling but not browned, add 3 tbs all-purpose flour and whisk continuously for 1 to 2 minutes to cook the raw flour taste, forming a blonde roux.
- 2
Add milk and season
Gradually whisk in 2 cups whole milk, pouring a little at a time to avoid lumps. Continue whisking until smooth. Bring the mixture to a gentle simmer, whisking frequently, until it thickens and coats the back of a spoon, about 4–6 minutes.
- 3
Finish sauce
Reduce heat to low. Stir in 1 tsp Dijon mustard, 1 tsp freshly grated nutmeg, 1 tsp salt, and 1 tsp freshly ground black pepper. Remove from heat briefly, then whisk in 1 cup grated Gruyère until melted and smooth. Taste and adjust seasoning. Keep sauce warm (low heat or cover) while assembling sandwiches.
Sandwich assembly and baking
- 4
Prepare bread
Preheat oven to 425°F (220°C). Lightly butter one side of each of the 8 bread slices with the 3 tbs room-temperature unsalted butter. Place 4 slices, buttered-side down, on a baking sheet or ovenproof skillet.
- 5
Assemble sandwiches
On each buttered bread slice (on the interior, unbuttered side up), divide 2 slices of ham evenly. Sprinkle about 1/4 cup grated Gruyère over the ham on each sandwich base. Top each with the remaining bread slices, buttered-side up, to form 4 sandwiches.
- 6
Top with Mornay
Spoon a generous amount (about 1/4 to 1/3 cup) of the warm Mornay sauce over the top of each sandwich, spreading slightly to cover the top crust. If using extra cheese, sprinkle 2 tablespoons (about 0.5 cup total divided) of additional grated Gruyère over the sauce for a gratin finish.
- 7
Bake to gratin
Place the baking sheet in the preheated oven and bake until the tops are bubbling and golden brown, about 8–12 minutes. For a deeper gratin, switch to broil for 1–2 minutes, watching closely to avoid burning.
Eggs (frying) and finishing
- 8
Fry eggs
While sandwiches bake, heat a large nonstick skillet over medium heat and add 2 tsp butter or neutral oil. Crack 4 large eggs into the skillet (work in two batches if needed) and fry sunny-side-up until whites are set but yolks remain runny, about 3–4 minutes. Season each egg with a pinch of the 1/2 tsp salt and 1/4 tsp black pepper.
- 9
Plate and assemble
When sandwiches are golden and cheese is melted, remove from oven. Using a spatula, transfer each sandwich to a plate. Gently place one fried egg on top of each sandwich.
- 10
Garnish and serve
If desired, sprinkle a little extra grated Gruyère and 1 tsp chopped fresh parsley over each sandwich. Serve immediately so the runny yolk mixes with the creamy Mornay and ham when cut.