For the chocolate glaze: Bring a medium saucepan full of water to a boil, then lower to a simmer. Combine the chocolate and the canola oil in a heat-proof bowl and set the bowl over the simmering water. Stir the chocolate and oil together until they are warm and completely melted. Do not allow the water to boil beneath the chocolate, and do not leave the chocolate unattended.
For the vanilla buttercream: In the bowl of an electric mixer fitted with the paddle attachment, paddle the butter on medium speed until it is soft and creamy. Add the confectioners' sugar and paddle the two together on medium-high speed until they are well combined and starting to fluff. Add the whole milk, vanilla and salt. Paddle on low speed to combine, then on medium-high speed until the frosting looks smooth and rich and creamy, 2 to 3 more minutes.
If preparing the buttercream ahead of time, store it in an airtight container at room temperature (about 72 to 75 degrees F is best) for up to 2 days. Otherwise, set it aside until ready to use.
For the sponge cake: Preheat the oven to 350 degrees F (or 325 degrees F if you have a convection oven).
Spray 3 jelly roll pans with nonstick spray. Line each with a piece of parchment paper and then spray again, making sure to coat the entire surface of the parchment paper lightly and evenly. Apply the same care to coating the edges of the pan with spray.
Bring a medium saucepan of water to a simmer.
Place the eggs and yolks in the bowl of an electric mixer. Whisk by hand to combine.
Add the brown sugar and vanilla and whisk again to combine.
Set the mixer bowl over the pot of simmering water and gently stir the eggs until they are warm to the touch and the sugar has dissolved. Do not whisk the eggs at this point and do not leave the bowl unattended.
Using the whisk attachment, whisk the eggs on medium-high speed until they are very light, fluffy and thick. This will take about 8 minutes
In the meantime, sift together the flour, cocoa and baking powder. Repeat the sifting two more times.
Fold the dry ingredients into the whisked eggs in three increments, being careful not to lose volume in the mixing.
Finally, drizzle in the warm melted butter and gently fold it into the batter. It is ok to lose a little of the volume at this point. However, be careful to not end up with a completely liquid batter as this will bake into a dry, flat sheet that is not pliable.
Spread about 2 to 2 1/2 cups of batter on to the prepared jellyroll pans. Bake the pans for 2 minutes, then rotate them half way and bake for another minute or two. They are done when you can lightly touch the surface of the sponge cake without leaving your fingerprint marked on the surface. Allow the cakes to cool for about 20 minutes.
When ready, dust the surface of each cake with granulated sugar and cover it with another piece of parchment paper. Gently, invert the tray onto your counter, releasing the sponge cake from the tray. Very carefully, peel the parchment paper away from the sponge cake and set the paper down over the cake again. Gently grab the edges of both the top and bottom sheets of parchment and flip the sponge cake back over so the top is facing up again. Now release the top piece of parchment paper from the sponge cake as well. Repeat with the remaining cakes. With a ruler and a steady hand, trim the edges of each cake so that you are left with a rectangle that is 9-by-15 inches in dimension. You are now ready to start filling and cutting your rollos.
Using an offset spatula, spread an even layer of about 1 1/2 cups vanilla butter cream on the surface of one of the sponge cakes. Use a little more frosting if you need to in order to cover all the edges evenly. Using a ruler and a long serrated bread knife or a long chef's knife, cut the frosted sponge cake into 10 rectangles each measuring 3-by-4 1/2 inches. Then, one by one, roll up the bottom of each frosted rectangle towards the top of the rectangle and wipe any excess frosting off of the sides of each rollo with the offset spatula. Place each finished rollo on a tray covered with parchment paper. When finished with all of the sponge cake, place the tray of rollos in the freezer and allow them to set for 30 minutes.
Re-warm the chocolate glaze at this point if necessary. It should be fluid and warm, but not hot.
Using two forks, one for dipping and one for balancing, dip each frozen rollo completely into the chocolate glaze. Lift it out from the chocolate glaze and tap the fork on the side of the bowl several times to force excess chocolate to drip off the rollo. Place each dipped rollo on another tray covered with a clean sheet of parchment paper. Proceed with the rest of the rollos, placing them a safe distance of about 1 inch apart. Refrigerate until set, about 30 minutes.
When the rollos are cold, gently lift them off the parchment paper to release them. Then trim the excess chocolate from each using a small sharp paring knife. Your rollos are now ready to be eaten and enjoyed. Ideally, they should be served as close to room temperature as possible, though some people prefer to eat these cold, or even frozen.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Elizabeth Belkind of Cake Monkey Bakery, Los Angeles, CA