Step 1

Heat oven to 355°F (180 degrees C. Butter a 9-inch/23 cm pie pan, cover the bottom with parchment paper, butter the paper, and set aside.

Step 2

Melt the dark chocolate in a microwave or water bath, set aside, and let it cool. The chocolate should be slightly warm to the touch.

Step 3

In a bowl, whisk butter and sugar with an electric mixer or a stand mixer until the mixture is creamy and the sugar is perfectly amalgamated. Add eggs (at room temperature) one by one, beating for about a minute each time. The mixture will become granular: it is all right.

Step 4

Reduce the speed to a minimum, pour the cooled melted chocolate, and mix until incorporated.  Keep the same low speed, add flour to the chocolate mixture, and mix until it disappears from the dough, but do not overmix!

Step 5

Pour the batter into the pan, smooth the top with a rubber spatula, and bake in the preheated oven for about 25 to 30 minutes. It may happen that the top will become cracked, and the cake will not look cooked entirely in the center, which is all right. Check the readiness of the cake: when you insert a knife in the center of the cake, some stained dough and moist crumbs will appear on the surface of the blade.

Step 6

Take the cake out of the oven and place it (still in the cake tin) on a wire rack and let it cool down. Once the cake has cooled at room temperature, refrigerate it for 1-2 hours to facilitate the removal of the cake.

Step 7

Next, turn the cake over, remove the parchment paper, and place it on a plate. Let the cake come to room temperature before cutting and serving.