1 lb purple potatoes
¼ cup olive oil (more or less)
1 tablespoon pitted and finely chopped Niçoise olives
1 teaspoon chopped parsley
1 can of packed sardines
1 teaspoon minced shallot
½ fennel bulb, fronds chopped off and reserved
1 hardboiled egg
Lemon juice
Salt and freshly ground black pepper

Basically there are three layers to the causa: purple potatoes mashed with the olives, sardines with shallots and capers, and thinly sliced fennel.
In a pot, cover the potatoes with ample water and bring them to a boil.
Cook until a knife can be inserted without any resistance.
Drain them of their cooking water and let them air dry and cool down.
In a bowl, fork mash them until they are thoroughly broken up. With a small whisk (or the fork if you do not have one), slowly pour in some olive oil. You will only use a few tablespoons of the olive oil in this, so just pour in a little at a time, and taste it as you go.
Add some salt if you like, and continue whisking until the potatoes are smooth.
Stir in the chopped olives and set aside.

Thinly slice the hardboiled egg crosswise and set aside.

Next, drain the sardines of their marinade and chop them up well. Combine them with the shallots, the parsley, some lemon juice, olive oil, and freshly ground black pepper.

Finally, slice the fennel thinly crosswise, so that there are transparent slices. Chop the fronds (what resembles dill), and toss them together with some lemon juice, salt, and olive oil.

Using a ring mold, or plastic half-pint container with the bottom cut out, layer the potatoes, egg, sardines, and the fennel salad in that order.
You can decorate with left over olives or capers as you like.
Makes 2 small causas (size of half-pint container).