1. Preheat your oven to 350 degrees F.
2. Make crust by whisking together the olive oil, coconut sugar, vanilla and sea salt. Add the flour(s) and stir everything together (Sarah says it should "feel like damp sand" at this point).
3. Use a piece of parchment (or rub a little olive oil on your hands) and press the dough evenly along the bottom and a bit up the sides of an 8-inch square or 9-inch round tart pan with a removable bottom (or use smaller, individual tart pans). Prick the crust all over with a fork and place in refrigerator until ready to bake, about 30 minutes.
3. After it has chilled, place the pan on a baking sheet and bake until golden brown and fragrant, about 25 minutes.
4. While the crust bakes, make the chocolate filling. Start by pouring the contents of one can of coconut milk into a medium bowl, and whisking it well so the thicker coconut cream is fully mixed with the thinner coconut water.
5. Measure out 1 cup of the coconut milk (refrigerate the rest and use in another recipe) and transfer it to a medium saucepan on the stove, along with 2 tablespoons sugar and a pinch of salt. Bring to a simmer, then remove from heat and add the chocolate. Allow chocolate to begin melting on its own, then stir it around until it is thoroughly combined with the coconut milk/sugar mixture.
6. Whisk the beaten egg into the chocolate filling (it will thicken), then pour everything into the hot crust. Turn oven temperature down to 300 degrees F. and return the tart to the oven.
7. Bake until the filling is set, but is still "a little wiggly" in the center, about 15 minutes. Sarah recommends checking after 13 minutes by "jiggling" the pan: only the center third should wobble. If it wobbles all the way to the edge, continue to bake for several minutes more. Note that the tart may take a bit longer to cook if you do use the coconut milk.
8. Remove the tart and allow it to cool before serving. After it's been out of the oven for 10-15 minutes, scatter sea salt across the surface. I used a large flake smoked sea salt for this: I broke some of the larger pieces up, but left others whole.
9. Remove tart from the pan sides and carefully transfer to a platter for serving. Sarah recommends letting it cool just until it slices easily, then serving it with a dollop of creme fraiche; I chilled mine and we ate it without adornment.