In a large pan over medium heat, add 1 tablespoon of butter and the spinach, and cook for a few minutes until the spinach has wilted. Set to one side to cool.
Drain the artichoke hearts and then chop them finely.
Wring out the cooled spinach to remove any excess water, and then finely chop.
In a large bowl, combine the artichoke and spinach with the cream cheese, ricotta, Parmesan, herbs, and garlic powder. Season with salt and pepper, to taste.
Heat a medium-sized saucepan to a medium heat and melt 2 tablespoons butter.
Whisk in the flour to make a roux.
Slowly add the milk to the pan, and then add the bay leaf and the nutmeg. Keep whisking until the sauce is smooth and thickened.
In a large lasagna dish, layer up the lasagna sheets, the artichoke and spinach mixture, and the béchamel, starting with a thin layer of béchamel so the lasagna sheets don't stick.
Top with the grated mozzarella and breadcrumbs, along with a little black pepper.
Bake in the oven for 45 minutes, until the lasagna sheets are soft and the top is golden.