The main difference between joconde and other sponge cakes is that it has whole eggs beaten into it, and not just whites. Observe:
6 room-temperature egg whites
1 ounce granulated sugar
8 ounces sliced blanched almonds, ground to powder in a food processor
8 ounces powdered sugar, sifted
6 large eggs
2.5 ounces all-purpose (AP) flour
1 1/2 ounces clarified butter, melted
Preheat your oven to 425 degrees Fahrenheit. Line two half-sized sheet pans (jelly roll pans) with parchment and brush with melted butter.
In the bowl of a stand mixer fitted with a whisk, whip the egg whites to soft peaks, add the sugar, and continue to whip to stiff peaks. Scrape the meringue into a bowl.
Wash the bowl of the mixer and dry it, and switch to the paddle attachment. Beat the almonds, powdered sugar and eggs on medium until they’re light and increased in volume, about 3 minutes. Turn the mixer down to low and add the flour, stirring just until it disappears.
Remove the bowl from the mixer and gently fold in the meringue. Lastly, fold in the clarified butter.
Divide the batter evenly between the two pans, spreading it as evenly as possible over the two pans. Bake for 5-7 minutes, until the layers are lightly browned. Remove from the oven and place the pans on the stove top. Cover each with a sheet of parchment, then flip the pans over on the countertop, thus turning the layers out. Carefully peel off the top layer of parchment, turn it over, and put it back on top of the layers until they’re cool.
The layers can be refrigerated for one day or frozen up to a month.