Bûche de Noël with chestnut cream

Preheat the oven to 400F (200C); brush parchment, cut slightly wider than the sheet, evenly with melted butter with no pools.

Separate the eggs and melt the butter for the génoise.

Whisk the sugar into the yolks until pale and fluffy ('blanch').

Sift in half the flour, then the rest; add half the melted butter, then the rest; sift in the cornstarch in two parts.

Whisk the egg whites with a tiny pinch of salt, slowly at first until foamy, then hard.

Fold the whites into the yolk mixture gently, lifting from the bottom of the bowl, until no pockets remain.

Spread the génoise batter evenly over the tray with a spatula and bake.

Dampen a towel and wring it out; as soon as the sponge is cooked, turn it out onto the towel, fold an inch crosswise and roll it up immediately so it does not break.

Cool the rolled génoise on a rack about 30 minutes.

Whisk the canned chestnut cream with soft butter and rum; break in three marron glacé and mix.

Syrup: bring sugar, water and rum to a simmer in a saucepan for five minutes, stirring to dissolve the sugar.

Unroll the génoise onto plastic wrap, brush it with the syrup, spread about two-thirds of the chestnut cream evenly and roll it up again using the plastic.

Set the log on foil-wrapped cardboard smaller than the platter.

Melt the chocolate in the microwave 15 to 20 seconds and mix it into the remaining chestnut cream for the icing.

Spread the icing over the log, leaving the ends bare; draw stripes with a fork.

Chill 5 to 10 minutes, then twist knots into the icing with a fork; press in marron glacé and garnish with silver pearls and edible gold.

Refrigerate at least two hours, then about another 10 hours.

Trim off the ends to show the layers, move to the platter, add a mint sprig and keep refrigerated until serving.