Preparation

• Melt the butter in a large (12-inch) skillet over medium-high heat. Add the asparagus, sprinkle with 1/2 tsp. each salt and pepper, and cook, stirring occasionally, until the spears start to brown and soften, about 3 minutes. Add the mushrooms and scallion whites and cook, stirring occasionally, until the mushrooms soften and cook through, about 2 minutes. Remove from the heat and let cool for a couple of minutes.
• Butter a 9×13-inch baking dish. Whisk the eggs with the milk and 1/2 tsp. each salt and pepper. Spread half the bread in a single layer on the bottom of the baking dish. Top with half the egg mixture and then cover with half the ham, cheese, and asparagus mixture, and sprinkle with half the scallion greens. Repeat with the remaining bread, custard, ham, cheese, asparagus mixture, and scallions. Cover with plastic wrap, pressing down so the bread is completely submerged in the egg mixture, and refrigerate for at least 4 hours and up to 2 days before baking.
• 将架子放在烤箱的中央，然后将烤箱加热到350°F。在烤箱加热时，让地层在室温下放置。烘烤大约30分钟，直到蛋ust套装和顶部棕色。松散覆盖箔，再烘烤20分钟。让冷却10分钟，切成平方块，然后食用。