1 cup (170g) semisweet or bittersweet chocolate chips
8 tablespoons (113g) unsalted butter, room temperature
3/4 cup (149g) granulated sugar
1/4 teaspoon salt
1 teaspoon vanilla extract, optional
3 large eggs
1/2 cup (43g) Dutch-process cocoa
Preheat the oven to 375°F. Lightly grease a metal 8″ round cake pan
Put the chocolate and butter in a microwave-safe bowl, and heat until the butter is melted and the chips are soft. Stir until the chips melt, reheating briefly if necessary. You can also do this over a burner set at very low heat. Transfer the melted chocolate/butter to a mixing bowl.
Stir in the sugar, salt, and vanilla.
Add the eggs, beating briefly until smooth. Add the cocoa powder, and mix just to combine.
Spoon the batter into the prepared pan.
Bake the cake for 25 minutes; the top will have formed a thin crust.
Remove it from the oven, and cool it in the pan for 5 minutes.