Direction :

1. Preheat oven to 325ºF and set a rack on the lower or middle level. Butter a 9-inch springform pan. Line the bottom of the pan with a circle of parchment paper.
2. Grind the almonds in a food processor with 1/3 cup of the sugar. (Post grinding, your almond-sugar mixture will be about 3 cups).
3. In a bowl over simmering water or in the top of a double boiler or in the microwave, melt the chocolate and butter together. Set aside.
4. Beat the egg yolks in a large bowl with an electric mixer until lemon-colored, about 5 minutes. Gradually beat in 2/3 cup of the sugar. Add the chocolate mixture, stirring to mix well. Add the ground almonds and stir to incorporate. Add the salt, and the 2 tablespoons of Grand Marnier, if using, and stir to combine.
5. In a clean bowl, beat the egg whites with the remaining 1/4 cup sugar until they form firm peaks. In two additions, fold the egg whites into the chocolate mixture.
6. Pour the batter into the prepared cake pan and smooth the top. Bake for 55 minutes to an hour or longer — a toothpick inserted in the center should come out clean or if you have an instant-read thermometer, it should register 205ºF or above. 
7. Let the cake cool in the pan on a wire rack for 15 minutes before removing the sides of the springform pan, then let cool completely.
8. When the cake has cooled, transfer it to a serving platter. Just before serving, sift confectioners’ sugar over the top.
9. Optional: beat 1/2 cup heavy cream with a few tablespoons of confectioners sugar and a pinch of flaky sea salt until soft peaks form — I do this with my flat-bottomed whisk (which I love: it’s the Xlarge Whipper). Taste. Add more sugar and/or salt to taste, and beat lightly again — I love whipped cream that’s still soft and billowy in texture and not too sweet. Serve each slice with a dollop of whipped cream and some fresh berries, if you have them.