Preheat oven to 400°F. Butter the bottom and sides of a 2 quart terrine dish.
Bring a large pot of water to boil and add the still frozen vegetables. Cook for 2 minutes, then remove from heat, rinse with cold water and drain completely.
Whisk the eggs together, then stir in the crème fraîche, drained vegetables, chopped herbs, salt and pepper. Pour 1/2 of this mixture into the prepared terrine.
Place the salmon filets in one layer on top of the egg mixture. You may need to slice the filets to fit to the dish. Pour on the remaining egg mixture.
Place the terrine in a deep oven proof dish and fill the outer dish with water. The water should come to a level just about even with the terrine dish. It may be easier just to place the dishes in the oven and then fill up with water from there.
Bake at 400°F for 1 hour.
Remove the terrine from the oven and allow to cool to room temperature. Cover in plastic wrap and refrigerate for at least two hours, but over night is best.
When ready to serve, slide a knife around the edge of the terrine, then turn out on to a serving dish. Serve cold slices accompanied by mayonnaise if you wish.
Makes 12 slices.