1. Preheat oven to 350 F. Lightly spray your baking dish with oil — see notes about recipe quantity and baking dish size.

2. In a small heat-proof bowl, melt chocolate and butter over a double broiler (a small saucepan with water, the bowl should not be touching the simmering water) set to medium-low heat on the stove. 

3. While chocolate is melting, separate eggs into two bowls – the yolks should be heatproof as well. If using a stand mixer, place the whites in that bowl and start whisking on low for 2 minutes, then medium for 2 minutes, then high, until stiff peaks form. 

4. Meanwhile, whisk the egg yolks and sugar together until the yolks turn from golden to a light yellow and it looks as if the sugar has fully dissolved. It may take about 4-5 minutes of vigorous whisking. The yolks should thicken a bit. (Alternatively, you can also do this in your stand mixer before mixing the egg whites. Just make sure you wash and clean the bowl well before whisking the egg whites). 

5. Once the chocolate is melted and smooth, temper the yolks and sugar by pouring just a small amount of the melted chocolate into them. Whisk while pouring. Then slowly add in the rest of the chocolate mixture to the yolks, while whisking. It may look like the chocolate seizes up, but keep whisking and it will smooth out. 

6. Once all the chocolate has been added to the yolks, take 1/3 of the whipped egg whites and fold into the yolk/chocolate batter. Once mixed well, add in the rest of the egg whites and fold gently again until there are no streaks or egg white clumps in your batter. 

7. Pour the batter into your prepared baking dish. Bake at 350 for 25 minutes (if using a small loaf pan) and check the center. If you want a more moist and fudgey center, allow for just a small amount of batter to stick to your toothpick or knife when inserted and removed from the center of the cake. If you prefer it more cake-y, bake for another 5 minutes or so until the knife or toothpick comes out clean. 

8. Allow to cool and then flip out onto a cooling rack. Store, covered in the fridge until ready to eat. Top with powdered sugar, raspberries whipping cream, or topping of your choice.