You can serve this koulibiac in hot plates with a slightly sharp sauce like a béarnaise or with a beurre blanc.
Remarks
When you make the koulibiak layers, don't hesitate to press each down to fill the dish well.
This recipe is not really difficult, but it's a bit long due as there are many ingredients to prepare. But most of them can be prepared in advance, the day before or so.
Salmon is not the main fish, the original recipe is made with pike, so you can easily substitute another of your choice.