1. Preheat the oven to 350 degrees F. Spray a large baking dish with oil and set aside.

2. Start by caramelizing the onions. Heat butter in a pan over medium heat add the onions stiring from time to time until the onions start to brown and caramelize about 12 minutes. Reduce to low if onions start to cook too fast. Once finished set a 1/3 cup aside to garnish.

2. To make the mornay sauce: In a small saucepan, melt butter over medium heat. Whisk in the flour and cook, stirring constantly, until you smell the flour and butter cooking, 1 to 2 minutes. Do not allow it to brown. Whisk in the milk and season with nutmeg and sage stirring constantly until the mixture thickens about 6 minutes. Remove from heat and add the shredded gruyere whisking to incorporate.

3. To assemble the croissants cut each piece in half lenghtwise to open them up to make a sandwich. Layer ham, onions, asparagus and drizzle with mustard. Place each sandwich into a baking dish placing them in different directions some facing out more. Pour the mornay sauce over top and in between the sandwiches finish with shredded gruyere and place more ham, asparagus, and onions pieces to fill any gaps. Bake for 20 minutes until the exterior start to get a little crispy and cheese begins to brown.

4. In the last few minutes of cooking start poaching the eggs.

5. To serve: serve each sandwich with a poached egg.