Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a mixing bowl, beat egg yolks with ¼ cup of sugar until thick and pale. In another bowl, sift together flour, cocoa powder, and salt.
In a separate bowl, beat egg whites until soft peaks form. Gradually add remaining ¼ cup of sugar, beating until stiff peaks form.
Fold egg yolk mixture into egg whites. Gradually fold in dry ingredients. Spread batter evenly on the prepared baking sheet.
Bake for 12-15 minutes, until the cake springs back when touched. Remove from oven and let cool slightly.
For the filling, whip heavy cream with powdered sugar and vanilla extract until stiff peaks form. Spread over the cooled cake.
Roll the cake into a log shape. For the frosting, beat butter until creamy. Gradually add powdered sugar, cocoa powder, milk, and vanilla extract. Spread over the rolled cake.
Decorate as desired. Chill before serving.