First you need to preheat your oven to 425ºF/230ºC.
Sift together your almond flour, first measurement of sugar and flour so you don't have any lumps.
Then you should blend in the 5 whole eggs into the flour until smooth.
In a separate bowl, whip egg whites to soft peaks and slowly add in the second measurement of sugar. Continue whipping to firm moist peaks. If they start crumbling you have over-whipped your egg whites and there isn't any way to save them.
Then fold your meringue into mixture until just combined. Make sure you don't over mix it or get too rough and break down all the air you built up in your batter or you'll have a very flat cake.
Slowly whisk in the melted butter.
Finally, spread the mixture onto your prepared silicone mat or parchment paper in a jelly roll or shallow sheet pan (13"x18)" and bake for 8 minutes. Make sure you don't over bake your cake.
Once your cake is cooled, sprinkle a thin layer of granulated sugar over the surface of the cake and cover with plastic wrap. Let sit overnight in the fridge. The sugar will dissolve into the cake as a result, the cake will stay moist even if it's exposed to air. Cool huh!
Tip for chocolate version: or a chocolate You will need to replace 35 grams of flour with 25 grams flour + 15 grams cocoa powder.