Preheat oven to 375 degrees F.
Line an 8” round cake pan (or pan of your choice--I like muffin tins) with parchment paper and grease with a non-stick spray. Keep ready.
Add the butter and chocolate into a microwave safe glass bowl and heat until the butter is melted and the chocolate is mostly melted. Stir the mixture until the chocolate fully melts. If you need to, reheat in 10 second intervals until you have a smooth consistency.
Add the sugar, salt and vanilla. Stir to combine. Add the eggs. Mix well.
Add the cocoa powder and gently mix until incorporated. Do not over-mix.
Pour batter into prepared pan and bake for approximately 20-25 minutes. The top may have slight cracks and form a crispy crust. The center should still be just slightly fudgy (but this isn’t a lava cake--so it shouldn’t be runny in the center).
Let the cake cool in the pan for about 10 minutes and then loosen the edges with a butter knife (use a plastic one if your pan is non-stick!)
Let the cake cool completely then top with powdered sugar, chocolate ganache, whipped cream or fruits before serving.