Preheat your oven to 300°F. Line the bottom of a 10-inch springform pan with parchment paper, ensuring it fits snugly. Lightly mist the inside of the pan with non-stick spray to prevent sticking. Set aside.

In a small saucepan, combine ¼ cup water, ¼ teaspoon salt, and ¾ cup sugar. Heat over medium-low heat, stirring occasionally, until the sugar has completely dissolved—this should take about 2–3 minutes. Once dissolved, remove from the heat and stir in 1 teaspoon vanilla extract. Let it cool slightly while you prepare the chocolate.

Place 12 ounces of chopped bittersweet chocolate and ¾ cup unsalted butter into a heatproof bowl. Melt using one of the methods listed below in the notes.

Pour the melted chocolate mixture into the bowl of a stand mixer. Beat on low speed for a couple of minutes to allow it to cool slightly. Slowly add the sugar syrup, mixing continuously. Next, add 4 whole eggs and 4 egg whites, one at a time, stirring until fully incorporated. The batter will be smooth and glossy.

Pour the batter into the prepared pan and smooth the top with a spatula. Bake in the preheated oven for 45 minutes. The center will still look wet, but don’t worry—this is normal! The cake will firm up as it cools.

Let the cake cool in the pan for 20 minutes before carefully running a knife around the edges. Transfer the pan to the refrigerator and chill for at least 4 hours (or overnight for best results).

Slice and serve chilled or at room temperature with whipped cream, fresh berries, or a scoop of ice cream. This cake is ultra-rich, so small slices go a long way!