3. In a separate large bowl, beat the egg yolks with 1 cup of sugar and vanilla extract until very thick and pale yellow - as you keep beating you will see them change color from the rich almost orangey-yellow of egg-yolk to a softer pastel yellow.
6. Add the whites and fold gently, but thoroughly, using a rubber spatula. This step was the most awkward for me, as the whites were hard to incorporate - but just be patient and keep folding the batter over the whites and it will eventually incorporate into a fluffy, somewhat lumpy, batter.
9. After you remove it from the oven, sprinkle the cake with rum.
10. Remove the cake from the pan by pulling it out on top of the parchment paper, and place the cake on the counter. Sprinkle the top of the cake with powdered sugar, and then place another piece of parchment paper on top of the cake (so the cake is now in the middle of a parchment-paper sandwich). Then take a cooling rack, or cookie sheet and place that on top of the top piece of parchment paper. Now is the tricky part - flipping the cake. We have a pizza peel on hand, and that worked wonderfully to flip the cake over with, but a thin cookie sheet, or just an extra pair of hands would help to flip the whole cake over so you can peel the buttered-parchment paper off.
11. While the cake is still warm, roll the cake, starting with one of the long edges, with the paper still on.
Ingredients for mocha buttercream:
- 1/2 cup water
- 1 1/4 cup sugar
- 5 egg yolks
- 1.5 cups (3 sticks) unsalted butter, softened
- 2 ounces unsweetened chocolate, melted and cooled
- 2 teaspoons instant coffee powder
Instructions for buttercream:
1. If you have not done so already, melt your chocolate. I use the double-boiler method: place a medium sized bowl over the top of a small sauce pan that has an inch or so of water in it. Bring the water to a boil. Once the bowl gets hot enough, you can place your chopped up chocolate pieces in the bowl and stir constantly until it is melted. Then remove the bowl from the pan and set aside. You can also melt chocolate in the microwave, but I am always afraid of burning it that way.
2. To ensure that the butter incorporated into the frosting well, I melted it in the microwave for about 30 seconds. It did not totally liquify, but it was very very soft.
3. Combine water and sugar in a small pot on the stove and bring to a boil. Boil for several minutes until the mixture reaches 238 degrees, or the mixture forms a soft ball when a drip is dropped into ice water.
4. While the water and sugar is boiling, beat the egg yolks until pale yellow. I started out doing this by hand, but got tired of all the beating so I switched to using my stand-mixer. A hand-mixer would work well too.
5. Once the yolks have reached the pale-yellow color, pour the hot syrup into the yolks, beating constantly (again, the stand mixer comes in handy here). Continue beating until mixture has cooled down significantly.
6. Beat the butter into the mixture, a little at a time, then add the melted chocolate and the coffee powder.
7. Depending on how warm the buttercream is, you might want to let it firm up a bit in the fridge before you start spreading it.
8. Once the buttercream is adequately chilled (to a frosting-like consistency) unroll the cake and spread the inside with half of the buttercream. Re-roll the cake as tightly as you can without breaking the cake (and if the cake does break a little, don't worry because it will be covered with frosting). To keep the cake "sealed" shut, I added a little extra buttercream along the top to make sure it did not unroll. If you have the time, cover the cake and let it chill for a couple of hours in the fridge. I only chilled mine for about an hour and it was fine.
9. Depending on the look you want, you can trim the edges off the cake and use them for decoration (or test-tasting) or you can leave the jagged edges on. Spread the roll with the remaining buttercream - I piled the remaining buttercream along the top of the cake and spread it down from there. Then score any kind of bark-like decorations into the cream you want. I let Jon do the decorating - he used the blunt end of a paint-brush to drag through the cream to make bark-grooves and a knot in the bark.
10. Depending on how fancy you want to get you can add marzipan leaves, almonds, cherries etc., and some people will cover the ends of the "log" in chopped nuts or colored sugar.