Recipe: Salmon Terrine with Spinach and Leeks

I was looking for a nice vegetable and fish terrine and couldn't find anything that suited me. So I took your salmon terrine as a base and drew heavily from it, which means I have no merit in this recipe.
I made it only once and somewhat by intuition. At the end, I added a few comments. You can see in the photo that the layers could be better distributed and better flattened.
Trim and cook the spinach for 5 minutes
Drain well (press with your hands)
Finely blend and put in a bowl
Slice the leek whites (washed) very finely. I start by splitting them in 4, if possible in 8 along the length then cut them finely.
Cook them covered with a piece of butter for about 30 minutes and put in a bowl
Carefully remove the bones and skin from the salmon
Finely blend it (raw). The fineness affects the final texture. Put in a bowl
In each bowl (spinach, leeks, salmon), add 100 g of cream, 2 egg whites or one whole egg, 2 g of agar-agar diluted in a teaspoon of water
Salt (about one teaspoon per bowl) and pepper. You can adjust by tasting.
In the salmon bowl, add one tablespoon of fish stock
Mix the contents of each bowl well
In a non-stick loaf pan or lined with plastic wrap or parchment paper, spread a layer of spinach over 1/3 of the height then a layer of salmon over 1/3 of the height and finally the leeks over 1/3 of the height.
Smooth each layer well with a spatula.
Preheat the oven to 350°F (180°C)
Place the pan in a dish filled halfway with water and put in the oven for 45 minutes once it reaches temperature.
Cover the pan with aluminum foil to prevent the top layer from browning (check from time to time)
When the terrine is cooked (insert a needle which should come out dry and hot), remove it from the water bath then wait 10 minutes before turning it out onto the work surface