Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish with butter.

Layer six slices of soft white bread in the bottom of the prepared dish, covering the base.

Spread half of the ham, turkey, and Swiss cheese on top of the bread layer.

Add the remaining six slices of bread on top and press down gently.

In a mixing bowl, whisk together the eggs, milk, Dijon mustard, and seasonings until smooth.

Pour the egg mixture over the casserole layers and gently press down to help absorb.

Cover the casserole and let it sit for at least 30 minutes at room temperature, or refrigerate overnight for maximum flavor.

Bake the covered casserole for 30 minutes, then uncover and bake for an additional 15-20 minutes until golden brown.

Allow to cool for 5-10 minutes, then dust with powdered sugar and serve with raspberry jam.