Preheat the oven to 350 degrees. Line a jellyroll pan with parchment paper. I also like to make sure and spray the edges of the pan to ensure an easy release. Set the pan aside.
In a small bowl, sift the flour, cocoa, baking powder, and salt. If you need to, sift it several times. You don't want any chunks in it!
Add eggs and sugar to a medium bowl. Mix on high for about 3-5 minutes. You will want the eggs to get frothy and light. Next is the vanilla, milk, and peppermint extract. I like to fold these in. Now with your flour mix, GENTLY fold it into the egg mix.
The batter is ready to bake. Pour spoonfuls across your jellyroll pan, then gently spread.
Place immediately in the oven on the middle shelf. Bake for 12 minutes, unless your oven runs hot, then reduce that time to 10-11 minutes.
While the cake is baking, prepare your tea towel. You do this by sprinkling generously with powdered sugar.
Once the cake has been baked, remove it from the oven. Run a knife around the edges, making sure it hasn't stuck. Invert your cake onto the powdered tea towel.
Carefully peel back the parchment to remove it. Starting at the short end, start rolling the cake, making sure to roll the towel in with it. Roll all the towel up with it.
Allow the cake to cool for about 2 hours. While it is cooling, prepare your filling below.
Once it has cooled, carefully unroll. Then with an offset spatula, spread the filling over the cake. This is enough filling to give it plenty of filling. Reroll the cake as tightly as you can without breaking it. Then, wrap tightly in saran wrap and place in the fridge. I chilled mine overnight, but I would say chill it for at least 4 hours.
Remove from the fridge and unwrap. Cover with the ganache, then sprinkle with the candy cane pieces.