Step 1

Preheat the oven to 400 degrees F. Grease a 3-quart casserole dish with butter.

Step 2

Whisk the eggs, heavy cream, cognac and some salt and pepper in a large bowl. Place the bread slices into the egg-cream mixture and let sit for 5 minutes.

Step 3

Cut the mushrooms into large dice and add to food processor along with the shallots and process until finely, finely chopped. Put a large cast-iron pan over medium-high heat and add 4 tablespoons of the butter. Once the pan is heated, add the mushroom/shallot mixture and cook until browned, about 5 minutes.

Step 4

Turn the heat under a medium cast-iron pan to medium-high and add the oil. Once heated, add the sliced spring onion and sear until browned on both sides, about 5 minutes total.

Step 5

To assemble, first put a third of the bread in the prepared casserole dish, then half of the mushroom duxelles, half of the seared onion and another third of the bread. Press down and top with the remaining mushroom duxelles and onions. Top with the remaining bread and dot with the remaining 4 tablespoons butter. Put into the oven and bake until golden brown, about 15 minutes.