Separate the egg yolks and whites. Mix the yolks with 1 1/2 tablespoons (20 grams) sugar, 3 tablespoons (40 grams) vegetable oil, 3 tablespoons (40 grams) milk, and a few drops of vanilla extract. Sift in the flour and cornstarch, then mix until smooth. Add a pinch of salt and a few drops of lemon juice to the egg whites, then beat until foamy. Gradually add the remaining sugar and beat on high speed until stiff peaks form. Gently fold a portion of the egg whites into the yolk mixture, then fold the yolk mixture back into the remaining egg whites until fully combined.

Preheat the oven to 340°F (170°C) for 10 minutes. Line a rectangular baking pan with parchment paper, pour in the batter, and tap the pan lightly to remove air bubbles. Bake for about 25 minutes. Once baked, remove from the oven, place a sheet of parchment paper on top, invert the cake, peel off the bottom paper, and let the cake cool completely.

For the chocolate coating: Break the chocolate into small pieces and place in a bowl with the butter and heavy cream. Set the bowl over a pot of simmering water and stir until the chocolate is fully melted and smooth. Let cool completely. Spread the chocolate over the cake, then refrigerate until the chocolate sets. Use a fork to create a tree bark effect, then decorate with snowmen, Santa figures, Christmas trees, or other decorations as desired.