Place potatoes in a large, heavy bottomed pot. Fill pot with enough cold water to cover potatoes and add yellow onion and garlic cloves.

Bring the pot to a boil over high heat. When boiling, reduce the heat to medium low and simmer until potatoes are cooked through, about 25 minutes. Use a knife to pierce the potatoes. If it goes through easily, the potatoes are cooked. Because you are using different sizes of potatoes, the smaller ones will be done in about 15 minutes. Remove them from the pot until all potatoes are cooked.

Turn off the burner, drain the water from the pot, add put the small potatoes back in the pot, return the lid to the pot, and allow the potatoes to rest and finish cooking for 15 minutes.

Peel potatoes and cut the bigger potatoes in chunks. Press first the potatoes and then the onion and garlic through a ricer or food mill into a large bowl and set aside to cool to room temperature.

While potato mixture cools, make the seafood salad. In a medium mixing bowl, flake the fish carefully with a fork. Remove any small bones. Add shrimp if using, scallions and chives if using.

In a small bowl blend the mayonnaise and Greek yogurt (if using), adding lime juice, vanilla extract, salt and pepper and paprika to taste. If you are using shrimp and fish, add another 1-1/2 tablespoons of mayonnaise or mayonnaise/yogurt blend to the salad.

When riced potatoes have cooled to room temperature, add 2 tablespoons vegetable oil, half of the remaining lime juice, and ají amarillo paste and continue to mix until potatoes are a uniform yellow color. Add salt to taste. Adjust lime juice and/or ají amarillo paste, if necessary. The flavor of the potatoes should be tart and somewhat spicy. If the mixture is dry, add in more oil, a teaspoon at a time, until the potato mixture holds together well.

Peel and slice avocado(s) and add a small amount of lime juice with the avocado to prevent discoloration.

Lightly grease the inside of a 9-inch springform pan with oil, being sure to coat the sides. Use your hands or a spatula to evenly spread 1/3 of the potato mixture inside the pan. (I found it helps to divide the potato mixture into two or three segments so that the layers will be equal sizes.)

If making 3 layers, add avocado slices, laying them lengthwise like a pinwheel over the potatoes. Fill the center with more avocado slices if necessary.

Very carefully add the next layer of the potato mixture using a spatula and hands. Gently press the potato mixture down.

Now, add the seafood on top of the potato mixture, then add the third layer of the potato mixture, again pressing very gently.

Cover the mold with plastic wrap and refrigerate to set Causa for at least 2 hours or up to 8 hours.

Before unmolding the Causa to serve, prepare the Salsa Golfo by blending the ingredients in a small bowl. You can drizzle the salsa onto the Causa with a spoon, but it’s a lot easier to use a small squeeze bottle and you won’t end up with blobs of salsa.

At the same time, prepare avocado slices, hard boiled eggs and olives for topping the Causa..

To unmold the Causa, remove the plastic wrap, and set the mold onto a serving plate. Run a flat spatula or knife carefully around the inner rim of the mold, then unlatch the mold and remove the outer ring. Using the spatula, smooth the top layer and sides of the Causa.

You can allow the Causa to rest before serving until it is a bit closer to room temperature. However, in hot weather, serve cold.

Decorate the top with olives, avocado and eggs. Squeeze the salsa onto the top layer.

To serve, cut the Causa as you would a cake.

Uneaten Causa will be good for another few days if you cover with the plastic wrap and return it to the refrigerator as soon as servings have been plated.