Preheat oven to 350°F / 175 ºC. Spray a 10x15 inch / 39 x 26 x 2 cm baking pan with nonstick spray or grease with butter. Line it with parchment paper and spray or grease it too, so the cake can easily unmold.

In a small bowl sift flour, baking powder, and salt.

Whip the egg whites with 1/4 cup / 50 g sugar on high speed until stiff peaks form, in a new bowl.

Beat yolks and remaining sugar on high speed until light in color. Then reduce to low and add buttermilk and vanilla extract. Increase the speed to high just until it's combined.

Add one part of egg whites to this mixture and mix. Then add the flour mixture and mix. Finally, add the remaining egg whites and carefully fold. Do not overmix.

Transfer the batter to the pan and spread it evenly and shake the pan to make sure it is leveled and reaches the corners. Bake for 12 minutes, until golden brown, and the toothpick comes out clean.

While cake is baking, lay a thin kitchen towel flat and sprinkle with sugar. When cake comes out of the oven, loosen it with a knife and immediately invert it onto the towel with sugar. Peel the parchment paper off and gently start rolling it from the narrow end with the towel so it doesn't stick to itself. Allow it to cool completely, you can leave it in the fridge for one hour.

While the cake cools prepare the filling.

In a food processor or a blender, grind freeze-dried strawberries into powder. Beat the cream cheese on high speed until completely smooth, then add sugar, vanilla, salt and crème fraîche and keep beating until combined. Fold in the strawberry powder and leave it in the refrigerator until needed.

Remove cake from refrigerator and let it sit for few minutes. Then, carefully unroll and flatten it out, so you can easily spread the filling evenly. Leave a 1/2 inch / 1 cm border around the cake without cream, this will prevent it from coming out. Gently roll it back up again, this time tightly and without the towel. Cover with plastic wrap and refrigerate again before serving. To serve, dust with confectioners sugar and you can garnish with fresh fruit if you like. To cut use preferably a bread knife.