3/4cupgranulated sugar,divided in half, plus more for sprinkling on parchment
3/4cupplus 1 tablespoon cake flour
3/4teaspoonfresh grated nutmeg
Fresh grated nutmeg and cinnamon
For the buttercream:
1/2teaspoonlight corn syrup
10ouncesunsalted butter,room temperature
Prepare the roulade:
Preheat the oven to 400 degrees F. Line a 13 x 17-inch jelly roll pan with parchment paper, lightly greasing above and below the parchment.
Whisk egg yolks with half the sugar and a splash of water to form a ribbon.
In a stand mixer with the whisk attachment, beat the egg whites and remaining sugar on high speed for one minute. Turn the speed down to medium-low and whisk until the egg whites reach a soft peak (the slower speed will form a more stable meringue). To tell when the whites have reached a soft peak, remove the whisk attachment and hold it with the whisk pointing upwards. The egg whites should form a peak that slightly droops at the top.
Fold 1/3 of the egg whites into the yolks with a spatula and combine well. Fold in the remaining whites.
Sift the flour into the egg mixture, folding to combine. Fold in the melted butter.
Pour the batter into the prepared pan. Use an offset spatula to spread the batter evenly. Then, clean around the edge of the pan with your thumb. Note: work gently but swiftly while folding the ingredients together and spreading them in the pan. The air in the whisked egg whites will make this cake very light and spongy, but the moment you begin working with the batter outside the mixer, it will slowly begin to deflate. The sooner it reaches the oven, the more volume your cake will have.
Bake for 7-10 minutes, until the cake is golden and spongy on top.
Loosen the edges of the cake with a paring knife. Sprinkle a generous amount of sugar onto a piece of parchment paper and invert the cake onto the sheet. Place a dishtowel on top and roll the cake tightly between the two pieces of parchment. Allow to cool for 10-15 minutes.
Prepare the buttercream:
In a stand mixer with the whisk attachment, whip the egg whites on medium speed until they form a stiff peak.
While the egg whites are whisking, add the sugar, water and corn syrup to a medium saucepan and cover. Bring the sugar to a boil. Remove the lid from the pan once steam has formed on the sides (this will prevent the sugar from crystalizing.) Insert a candy thermometer and cook the sugar until it reaches 235-240 degrees F.
Once the egg whites have reaches a stiff peak, turn the speed to low and carefully pour the sugar syrup down the inside of the mixer into the meringue. Don't pour too quickly or the eggs will scramble. This is called an Italian meringue.
Whip the meringue on high until it comes back to room temperature. This process will take 20-30 minutes.
When the meringue is cool and at a stiff peak, add chopped butter, one piece at a time, with the mixer on medium-low.
Turn the mixer speed up to high and slowly add the eggnog and rum. Add a few tablespoons at a time and wait until the liquid is fully incorporated into the buttercream before adding an additional more. Repeat until all of the liquid is incorporated. If you add the liquid too quickly the buttercream will deflate.
Assemble the roulade:
Gently remove the parchment from the cake. Use an offset spatula to spread the buttercream on the cake as evenly as possible.
Re-roll the cake tightly. Slice off the edges for a clean presentation. Garnish with fresh grated nutmeg and cinnamon.