Heat the oven to 350 degrees. Butter an 8-inch spring form pan and line the bottom with a round of parchment paper cut to fit.
In a large bowl, whisk together the sugar, cocoa powder, and salt. Pour the melted butter into the mixture and whisk until smooth.
Whisk in the eggs one at a time, then the vanilla. Whisk in the flour until smooth.
Scrape the batter into the prepared pan, smoothing the top. Bake until the top of the cake is just firm, the edges are puffed and the center jiggles thickly when you shake the pan. 30 to 40 minutes. Err on the side of underbaking so that the center is a little running when you cut it. Transfer to a wire rack to cool completely. At least two hours.
Release the sides of the springform pan and remove them. Place the torte, still on the bottom of the pan on a cake plate. Sprinkle with cocoa powder through a sieve. Serve with ice cream or whipped cream.