Preheat oven to 350°F (177°C). Grease a 9×2-inch round cake pan, line with a parchment paper round, then grease the parchment paper. Parchment paper helps the cake seamlessly release from the pan. (If it’s helpful, see this parchment paper rounds for cakes video & post.)

In the bowl of an electric handheld or stand mixer fitted with a paddle attachment, cream the sugar and butter together on medium speed until light and fluffy, about 3 minutes. (Here’s a helpful tutorial if you need guidance on how to cream butter and sugar.) With the mixer on low, slowly stream in the oil. Scrape the sides and bottom of the bowl to make sure everything is well blended. With the mixer on low, add in the eggs, one at a time, making sure that each is incorporated before adding in the next. Add the vanilla and run the mixer for 30 more seconds. Take the bowl out of the mixer.

In a medium bowl, whisk the flour, cocoa powder, baking powder, baking soda, and salt until combined. With a silicone spatula or wooden spoon, fold the flour mixture into the butter mixture in three batches, mixing each until almost blended. Batter will be very thick. Finally, pour in the hot water and whisk to combine. Pour evenly into prepared cake pan. Lightly tap pan on the counter a few times to settle the cake batter and release any trapped air bubbles.

Bake in the center of the oven for 30-36 minutes (and up to 40 minutes, if needed but begin checking at 30). The cake is done when a toothpick inserted into the center comes out clean or when the cake springs back if you lightly poke the center with your finger. Remove from the oven and cool cake in the pan set on a cooling rack for 20 minutes. Remove cake from the pan and place cake directly on the cooling rack to finish cooling. Once cool, you can place the cake on your cake stand or serving plate.

Place the chocolate, cream, and salt in a large heat-safe bowl set over a medium saucepan of simmering water. (Or use a double boiler if you have one.) Do not let the bottom of the bowl touch the water. Stir frequently until chocolate has melted and ganache is smooth. Remove from heat and stir in the vanilla. Set aside at room temperature to cool until thickened. You want it cool enough to not melt the frosting, but still a little fluid. This takes about 60-90 minutes to cool. (NOTE: This yields a lot of ganache and I used about 3/4 of it on top of the cake and then drizzled more on each slice.)

In the bowl of an electric handheld or stand mixer fitted with a paddle attachment, beat the butter, shortening, and mint together on medium-low speed until combined. Scrape down the sides and up the bottom of the bowl and beat again as needed to combine. Add confectioners’ sugar, peppermint extract, and milk and continue beating until whipped, smooth and creamy.

Spread peppermint cream in a thick layer all over the top of the cooled cake. There’s a lot of frosting, so pile it high. Try to make the edges sharp angles that follow the line of the cake. (You can see it pictured above.) I always use a small icing spatula. Place uncovered in the refrigerator for 30 minutes to help set the frosting. Pour ganache slowly on top of cake and use a small offset spatula or a knife to gently spread all over the frosting. Return cake to the refrigerator and chill uncovered for 30 minutes before slicing and serving. Feel free to garnish with mint leaves.

Cover leftover cake tightly and store in the refrigerator for up to 1 week.