Preheat the oven to 350˚F (175˚C). Generously grease the bottom and sides of an 8-inch cake pan. Line the bottom with a round of parchment paper and grease the paper.
Place the chocolate in a heatproof bowl and microwave it in 15-30 second intervals, stirring between each, until melted (alternatively, melt the chocolate on the stovetop in a bowl set over a pot of simmering water or in a double boiler). Let it cool for five minutes.
In a stand mixer with the paddle attachment (or using hand beaters), combine the eggs and sugar. Beat on high until light in color and doubled in volume, about 2 to 3 minutes (this is an important step, as there are no other leavening agents in the cake). Mix in the salt and vanilla. With the machine running on medium, slowly pour in the chocolate. Stop and scrape down the sides (the batter will have speckles of chocolate, which is okay), then add the almond flour. Mix on low until just combined. Give the batter one more fold with a rubber spatula to incorporate any flour on the sides.
Transfer the batter to the prepared pan and spread the top in an even layer. Bake for 24-26 minutes, or until the top looks dry and a toothpick inserted in the center comes out with few damp crumbs (the toothpick shouldn’t come out clean—err on the side of under-baking). Set the pan on a cooling rack and let it cool for 10 minutes.
Run a thin knife or small off-set spatula around the edge of the pan, then invert the cake to remove it from the pan. Peel off the parchment, then invert the cake back on the rack, top side up, and let it cool completely. Cut the cake into slices, and serve it on its own, or with fresh berries and whipped cream.