Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a mixing bowl, beat egg yolks with ¼ cup sugar until thick and pale. Add vanilla extract.
In another bowl, sift together flour, cocoa powder, and salt. Gradually add to egg yolk mixture.
In a separate bowl, beat egg whites until soft peaks form. Gradually add remaining ¼ cup sugar and beat until stiff peaks form.
Gently fold egg whites into the yolk mixture. Spread batter evenly on the prepared baking sheet.
Bake for 12-15 minutes, or until the cake springs back when lightly touched.
While the cake is baking, prepare the filling. Whip the heavy cream with sugar and vanilla extract until stiff peaks form.
Remove the cake from the oven and immediately roll it up in a clean kitchen towel. Let it cool completely.
Unroll the cooled cake and spread the whipped cream evenly over the surface. Roll the cake back up.
For the frosting, mix cocoa powder with a little water to form a paste. Add to remaining whipped cream and mix until smooth. Spread over the rolled cake.