Preheat oven to 375 F and grease an 8" cake pan.
Melt butter and chocolate in a small saucepan over low heat, stirring constantly until smooth.
Remove from heat and let cool for a few minutes.
Transfer to a mixing bowl.
Stir in sugar.
Add the eggs and mix.
Stir in cocoa powder.
Pour the batter into greased cake pan and bake for about 20-25 minutes.
Cool the cake in the pan for 5-10 minutes, then flip out onto a plate, and carefully flip from the plate onto a cooling rack (this keeps the top of the cake smooth and shiny).
Serve warm with ice cream, or cool completely and dust with powdered sugar or top with whipped cream.
Slice and indulge!