Joconde biscuit is an almond sponge pastry classic, used as a base for many desserts and entremets. Makes two 18''x13''/46x33cm sheets. Preheated oven to 450ºF/230ºC 10 min before finishing biscuit. In the bowl of a stand mixer fitted with the whisk attachment, beat egg whites along with cream of tartar and half of sugar (15g) on high speed and whip until stiffness is achieved adding remaining sugar gradually. Transfer meringue to a clean large bowl and set aside. In the same bowl ; no need to clean it, combine the powders with the eggs, and beat on high speed for about 5 minutes or until pale yellow. Gently, fold one-third of the meringue into the almond mixture and add remaining meringue. Fold in melted butter but not hot. Spread evenly over baking trays lined with lightly oiled silicone mat, or parchment paper.
Bring to boil and cool. Refrigerate for up to 2 weeks.
(Crème Anglaise Method). Bring milk, sugar and vanilla to a boil. In a separate bowl, beat egg yolks and sugar. Remove from heat and whisk in one-third of the milk into the yolk mixture. Then, gradually add the remaining milk, whisking constantly. Return custard to the stove, gently heat the mixture to just below the boiling point 185ºF/85ºC, it will thicken. Do not boil or the eggs will curdle. Check to see if it is the right consistency by holding a spatula that is covered with the custard and run your finger along the back of the spoon. If the streak remains without the cream running down through the streak, it is ready. Immediately remove from the heat and pour through the strainer hanging over a mixer bowl. Beat on high speed until the crème Anglaise cools to room temperature. Add the softened butter and whip until creamy and fluffy on high speed. Fold in the Italian meringue (optional); it improves the texture. Use right away. This buttercream can be kept refrigerated for several days or frozen for up to 3 months. Bring to room temperature and whip again before reusing it.
Get the biscuit ready (skin side up). Brush some vanilla simple syrup and spread about half of the buttercream evenly. Roll out lengthwise to create the most layers (tree rings). Brush more sirup on the surface of the log. Freeze or refrigerate until firm. Cut off edges to create knots. Frost the log completely with remaining buttercream using a tip start pastry or a spatula. Use a fork to create design resembling tree bark. Add Xmas decorations if desired. Pull log from refrigerator 30 min prior serving. Merry Christmas🎅🏻