½cup(113g)salted butter, cut into tablespoon-size pieces
2tablespoonvegetable, canola, avocado or grapeseed oil
1 ⅔cups(283g)semisweet chocolate chips or chopped chocolate (see note)
2tablespoonsnatural unsweetened cocoa powder
¾cup+ 2 tablespoons granulated sugar, divided (you'll use 1/4 cup in the batter, 1/2 cup in the egg whites and 2 tbsp on top of the batter)
¼teaspoonsalt, I use coarse, kosher salt
Sweetened whipped cream
Hot fudge sauce or chocolate ganache drizzle, see note
Preheat oven to 350 degrees F. Lightly butter the bottom and sides of a 9-inch springform pan. Dust with 1-2 tablespoons granulated sugar and shake to lightly coat the bottom and sides; tap out any extra sugar.
In a medium microwave-safe bowl, combine the butter, oil, and chocolate. Microwave for 1-2 minute intervals at 50% power until the mixture is melted and smooth (don't overheat!). This can also be done in a heatproof bowl set over a pan of simmering water. Set aside to cool to room temperature.
Separate 4 of the eggs, placing whites and yolks in separate medium size bowls. Make sure not to get any bits of yolk or shells into the egg whites or they won't whip to stiff peaks.
To the egg yolks, add the remaining 2 whole eggs, cocoa powder, 1/4 cup granulated sugar, vanilla, and salt. Whisk until the mixture is well-combined. Pour the egg yolk mixture into the bowl with the melted chocolate/butter mixture and whisk until smooth.
Using an electric mixer on high speed, beat the egg whites until foamy, about 30 seconds. With the mixer running, gradually add 1/2 cup granulated sugar and continue mixing until stiff, glossy peaks form (the peaks should hold their shape as the mixer is lifted out of the egg whites).
Add half of the egg whites to the chocolate batter and fold gently with a rubber spatula until partly combined (a few streaks is fine; don't whisk or mix too vigorously or the egg whites will deflate). Add the remaining egg whites and fold gently until just incorporated and no white streaks remain.
Scrape the batter into the prepared pan and smooth the top. Sprinkle the top with 2 tablespoons granulated sugar (optional).
Bake the cake until the top is puffed and starting to crack and the cake is pulling away from edge of pan just slightly, 25-30 minutes. Don't overbake! Let the cake cool completely in the pan. The middle of the cake will fall as it cools. Serve warm, at room temp or chilled. The cake can be made 1-2 days ahead of time and refrigerated.
Top with sweetened whipped cream, fresh berries and hot fudge sauce or chocolate ganache (see note).
Nutrition Facts: the nutrition facts for this recipe were calculated based on the cake (but do not include the toppings as those are added based on personal preference). Chocolate: good quality chocolate is key here because that chocolate flavor is paramount with such a simple list of ingredients. I would recommend using Ghirardelli, Guittard or Callebeaut semisweet chocolate chips. Bittersweet chips could probably be used, but depending on the %, you might need to add a touch more sugar to the batter.Whipped Cream: for the sweetened whipped cream, I add 1 1/4 cups heavy whipping cream + 2-4 tablespoons powdered sugar to my blender and mix until thick and creamy (can use an electric stand or handheld mixer).Chocolate Drizzle: this hot fudge sauce would work great, but for a simpler version, combine 1/2 cup chocolate chips + 1/2 cup heavy cream in a microwave-safe bowl and heat just until warm. Let sit for a minute or so and then stir to combine until smooth and glossy (for a thinner consistency, add 3/4 cup cream to start).