Peppermint Chocolate Cake Roll

I have been meaning to write up this recipe for weeks!  I pinned this amazing dessert about a year ago and couldn't find the right opportunity to make it until this year's office holiday party.  It was a HIT.  I was also reminded of Buche de Noel (Yule Log).  While this really isn't one (different ingredients, not at all decorated like a log, etc.) it still fits the bill of "cake filled with nummy icing and rolled up."
Part of the reason I wanted to write this up is because the original pin is a bit of a wild goose chase taking you to two different pages in order to make everything.  It will be nice to have this all written up in one spot, along with notes from my experience (e.g., don't let the cake hang around in your fridge for a day).

We'll talk about the rectangle shape later in the post.  But believe me, it tasted amazing.

Ingredients
Cake

• 5 tablespoons unsalted butter, plus more for parchment and pan
• 2/3 cup sifted cake flour (not self-rising)
• 1/3 cup sifted cocoa powder, plus more to dust cake for handling
• Pinch of baking soda
• 6 large eggs
• 3/4 cup sugar
• 2 teaspoons vanilla extract

Peppermint Buttercream Frosting

• 12 tablespoons unsalted butter (1 1/2 sticks)
• 5 tablespoons heavy cream
• 2 cups confectioner's sugar
• 1/2 cup chopped Peppermint Andes (I used the Peppermint Crunch ones), plus more Andes to finely chop/shave for cake topping

Chocolate Pouring Sauce

• 2/3 cups dark chocolate (1 large chocolate bar, chopped)
• 2 tablespoons heavy cream
• 4 tablespoons confectioner's sugar, sifted
• 4-5 tablespoons warm water

Directions

Cake

1. Heat oven to 350°.  Butter a large Pyrex dish (mine is 11" x 15").  Martha Stewart's cake recipe recommends a 10.5" x 15.5" x 1" jelly roll pan.  I'm not a fan of using specialty pans/equipment for a one-time recipe, so I just used my large Pyrex and it worked just fine.
2. Line with parchment paper.  Butter the paper and coat with flour, tapping out the excess flour.
3. Sift flour, cocoa, and baking soda together twice into a medium bowl then set aside.  Now, this step is deceptive because I actually needed two bowls.  I sifted the mixture into bowl #1, but then needed to pour the mixture back into the sifter and sift again, without losing any of my mixture.  I just placed a small bowl under the sifter to catch any mixture that fell through during transfer, then resumed sifting into the newly-empty bowl #1.
4. Melt butter in a small saucepan over low heat.  Skim off the white foam with a spoon, and pour the clear yellow butter into a small bowl, discarding leftover white liquid at the bottom.  Set aside in a warm place (like on top of the preheated oven).
5. Set a small pot of water to simmer.  In a medium heat-proof bowl that will fit on top of the pot without touching the water, whisk together the eggs and sugar.  Set the bowl over the simmering water, and stir mixture until it is warm to the touch and sugar has dissolved (3-5 minutes).  Remove from heat, and beat on high speed in a stand mixer until thick and pale and has tripled in bulk, 5-7 minutes.  Reduce speed to medium, add vanilla, and beat 2-3 minutes more.
6. In three additions, gently fold flour mixture into egg mixture with a spatula.  While folding in the last addition, dribble melted butter over the batter and fold in.
7. Spread batter evenly in pan, leaving behind any unincorporated butter in the bottom of the mixing bowl.  Tap Pyrex dish on counter several times to remove air bubbles.  Bake until cake springs back when touched in the center, 15-20 minutes.  Don't overbake or cake will crack.  Let sit in pan on wire rack until cool enough to handle (~1 hour or more).
8. Dust surface with cocoa powder.  To make rolling easier, run a knife along the edge of the cake to loosen from the Pyrex dish.  Cover cake with a sheet of waxed paper and a clean, damp dish towel.  Invert onto a work surface, and peel off the parchment paper from the bottom of the cake.  Dust with cocoa powder.  Starting from one long end (the 15" side, not the short 11" side), carefully roll up the cake in the towel.  Wrap in plastic and refrigerate until ready to use, but no more than a couple hours.  If you let the cake sit for a day or more, it is going to harden more into its shape and be difficult to roll later, hence the odd rectangle shape I got rather than a nice circular roll.  Still, it all tastes the same in the end so don't sweat it too much.

Peppermint Buttercream Frosting

1. Place all ingredients in a bowl and beat until smooth.  Try not to eat it all.

Chocolate Pouring Sauce

1. Place chocolate and heavy cream in a bowl over simmering water.  Let chocolate and cream sit for 2-3 minutes to melt without stirring.  Then slowly stir mixture until well combined.  Add confectioner's sugar and mix to combine.  Add water 1 tablespoon at a time, mixing after each addition, until pouring consistency is achieved.  It should be the texture of chocolate syrup (not watery).  Set aside and let cool until it is merely warm (not hot).

Assembly

1. Unroll the chocolate cake and spread with buttercream filling, to about 1/4" thickness.  Make sure you spread filling evenly over entire cake.  Roll filled cake from long end to long end, just as you did when you chilled it.  Trim ends for clean finish (and so you can get the very important tasting pieces).
2. Place fully assembled roll on a serving platter (or on a cooling rack if you want to pour the chocolate sauce, then transfer to another plate for serving with a clean presentation, which I clearly did not do).  Pour chocolate on top.
3. Sprinkle with peppermint Andes shavings.

So. Delicious.