Grease a 9x13 inch ceramic baking dish with butter or non-stick cooking spray.
Distribute half of the bread cubes evenly across the bottom of the prepared dish.
Layer the diced ham and shredded Swiss cheese over the bread cubes in an even layer.
Top with the remaining bread cubes, ensuring even coverage.
In a large mixing bowl, whisk together the eggs, milk, heavy cream, vanilla extract, nutmeg, and salt until fully emulsified.
Pour the egg mixture slowly over the bread layers, ensuring all bread cubes are moistened. Press down lightly with a spatula to assist absorption.
Cover the dish and refrigerate for a minimum of 2 hours, though overnight is preferred for optimal texture.
Preheat the oven to 350°F (175°C).
Bake uncovered for 40 to 45 minutes, or until the custard is set and the top cubes are golden brown and crisp.
Remove from the oven and allow to rest for 5 minutes. Dust heavily with powdered sugar and serve warm with a side of raspberry preserves.