Place a rack in the middle of the oven; preheat to 350°. Brush the pan with vegetable oil, making sure to cover the sides to the brim. Line bottom of pan with a round of parchment paper; brush the parchment with oil.
Heat 10 oz. (283 g) semi-sweet chocolate (64–70% cocoa), coarsely chopped, 6 tablespoons grapeseed, avocado or other neutral oil, ¼ cup strong brewed coffeeY 1½ tsp Diamond Crystal or ¾ tsp. Morton’s Kosher Salt in a large heatproof bowl set over a medium saucepan of simmering water (bowl should not touch water), stirring occasionally with a heatproof rubber spatula, until chocolate is melted and mixture is smooth , approximately 5 minutes. Remove bowl from heat; add 5 large egg yolks, room temperature, 2 teaspoons vanilla extractY ¼ cup (50 g) granulated sugar and beat vigorously to combine. Add ¾ cup (72 g) almond flour or almond grits and mix well. (Don’t worry if it looks torn and separated.) Add ¼ cup of water and shake vigorously until the mixture comes back together and looks smooth and glossy. Set the chocolate mixture aside.
Using an electric mixer on medium-low speed, beat 5 large egg whites, room temperatureand a pinch of salt in a large non-plastic bowl until frothy, about 20 seconds. Increase speed to medium-high and continue to beat until foamy and opaque, about 30 seconds. Whisking constantly, gradually add the rest. ¾ cup (150g) granulated sugar in a slow and steady flow. Increase speed to high and beat until stiff peaks form and meringue is thick and glossy. (Be careful not to over-beat or it will be dry and grainy and difficult to incorporate into the batter.)
Scoop out a heaping cup of meringue and set aside. Scrape about half of the remaining meringue into a bowl with the reserved chocolate mixture and mix gently with a spatula until just a few streaks remain. Scrape up remaining meringue; fold until evenly mixed and dough is light and airy. Scrape dough into prepared pan; smooth surface. Spoon reserved meringue over dough. Using a skewer or toothpick, stir them into the batter, a little or a lot; up to you.
Bake the cake until the surface rises and cracks, the meringue is lightly browned, and a tester inserted into the center comes out shiny but clean, 60 to 70 minutes. Transfer to a wire rack and run a small knife or offset spatula between the top of the cake and the pan to loosen any places where it might be stuck (this will help the cake set evenly as it cools). Let the cake cool in the pan.
To serve, run knife around sides again to loosen cake, then unmold.