To the Mashed Potatoes, add the Caramelized Onions and Gruyere, reserving 2 tablespoons of each for garnish. Transfer to a serving bowl and garnish with the crushed Croutons and the reserved cheese and onions.
In a large saucepan, combine the potatoes, 1 teaspoon salt and enough cold water to cover. Bring to a boil over high heat. Lower the heat to maintain a simmer, and cook until fork tender, about 10 minutes.
Drain the potatoes and return to the pan. Shake the pan over medium heat for about a minute to dry the potatoes. Transfer the potatoes to a food mill, ricer or bowl.
Put the milk and butter in the saucepan and heat over medium-high heat until the butter melts and the milk is hot. Remove the pan from the heat. Mash the potatoes through the food mill, ricer or by hand into the pan. Stir to combine with the milk and butter. Season with salt and pepper, and add nutmeg if desired. Serve immediately.
Melt the butter in a large skillet over medium heat. Add the onions and toss to coat with butter. Cover and slowly cook onions, stirring occasionally, until golden, 10 minutes. Turn the heat up to medium high and begin to brown the onions, stirring constantly, about 10 minutes more. Season with salt and pepper.
Preheat the oven to 350 degrees F. Whisk together the butter, olive oil, oregano and garlic salt, and toss with the bread cubes. Spread in a single layer on a baking sheet. Bake until golden brown and toasted, 15 to 20 minutes.