Put the butter in a heatproof dish and microwave for about 40 seconds until it's completely melted. Preheat the oven to 180ºC.
Separate the whites and yolks of the eggs. Put the egg whites into a large bowl.
Beat the egg whites, adding the granulated sugar in 3 batches. Beat until stiff peaks form.
If using a hand mixer, beat on low speed for the last 30 seconds to give the batter a good texture.
Add the egg yolks and mix gently. Switching to a rubber spatula, sift in the cake flour and fold in lightly.
Add the butter and mix gently to combine. Pour the batter into a baking sheet lined with parchment paper. Smooth out the surface of the batter.
Drop the baking sheet 4 or 5 times onto a flat surface from a height of about 10 cm to remove air bubbles. Bake for 10 minutes in the preheated oven.
When it's done baking, drop the baking sheet once more as you did in step (7). Pull on the sides of the parchment paper to remove the cake from the baking sheet. Let cool.
Put the heavy cream and the sugar in a bowl and whip well. If the cream is too soft, it will seep out when you cut the cake, so make sure to whip until it's hard enough!
When the sponge cake has cooled, cut off the end diagonally.
With the browned side of the cake facing up, spread plenty of whipped cream on the cake. Use a lot of whipped cream on the edge closest to you and use a smaller amount as you get to the end with the diagonal cut.
Take the edge closest to you, fold it over and roll towards the center. Gently and neatly roll up the cake.
When you're done rolling the cake, adjust the shape. Wrap in plastic wrap and place in the refrigerator, seam side down. Let rest in the refrigerator for at least 1 hour.
Slice as thick as you prefer, and enjoy!
Story Behind this Recipe
I did a lot of experimenting and finally came up with a recipe for roll cake that won't break when you roll it up. This is a very simple roll cake. I think you'll like it!
Make sure you beat the egg whites very well. If you don't want the surface of the cake to become browned, cover the cake in plastic wrap immediately after baking and the color will come off when you remove the wrap.