Slice bread into long slices, about 1/3" thick.

You should have 6 or 7 slices.

Arrange 3 of the slices in one layer in the buttered pan.

Top with half the corned beef.

Cover with half the cheese, onions and half the herbs.

Arrange 3 more slices of bread over this (it doesn't matter of the bread doesn't fit snugly, although you can use the extra slice to fill in any gaps).

Arrange remaining gruyere, cheese and herbs over bread.

In a mixing bow

Whisk eggs until combined.

Add milk, mustard, salt and pepper and whisk until light and frothy.

Pour egg mixture evenly over bread, using the entire mixture.

Cover with plastic wrap and refrigerate overnight.

When ready to bake, pre-heat oven to 350? F.

Bake the pudding on the bottom rack in the pre-heated oven for 1 1/2 hours until puffed and browned.

Let pudding rest for 15 minutes before cutting into squares.