Make the cupcakes:

1. Preheat your oven to 350F and place liners in your cupcake tin.
2. In a large bowl, whisk together flour, sugar, baking soda, cocoa powder, and salt.
3. Stir in oil and sour cream. Gradually add in water. (I like to do this in 4 installments, whisking between each to combine.)
4. Add vinegar and vanilla. Whisk in eggs, one at a time. Continue whisking until everything is combined.
5. Divide batter evenly between your cupcake liners, leaving a small space at the top to allow for rising. Bake for about 20 – 30 minutes. You’ll know they’re done if when gently pushed the cake springs back. Let cool for about 10 minutes in the pan, then cool completely on a wire rack before filling.

Make the ganache:

1. Put your heavy cream in a microwave-safe bowl and heat gently for 30 seconds in the microwave. (I stop it at 15 seconds to make sure it isn’t scorching.)
2. Once heated through, pour in about one-third of your chocolate chips and stir with a rubber spatula until melted. Add in the rest of them and continue stirring until the mixture is smooth and shiny. Add in the peppermint extract and stir.
3. When your cupcakes are totally cool, use a small cookie cutter (I use a 1″ guy) to carefully core out your cupcakes. They are very soft, so be careful not to rip the tops off. Once the ganache is cool but still spoonable, spoon the mixture into the cupcakes. It will still be fairly liquid, so pop the filled cupcakes in the fridge to cool for about 10 minutes to firm up.

Make the frosting and assemble:

1. Put your egg whites and sugar in the bowl of a stand mixer and give it a quick whisk by hand to combine.
2. Create a double boiler by filling a saucepan with a few inches of water and setting over med. heat. Remember, don’t overfill your saucepan, you don’t want your stand mixer bowl to touch the water.
3. Set the stand mixer bowl over the saucepan, and whisking occasionally, bring your egg and sugar mixture to 160F. (If you don’t have a candy thermometer, use your finger and pull the bowl off when the mixture is hot to the touch.)
4. Attach your now-heated bowl to the stand mixer (careful, she’s hot.) With the whisk attachment, whisk the mixture on high speed until it holds medium-stiff peaks. This can take up to 10 minutes, so be patient, by the time it’s done, your bowl should be back to room temperature.
5. Trade your whisk out for the paddle attachment and with the mixer on low, begin adding the butter, a few cubes at a time. Add the peppermint extract and beat until silky, roughly 3 minutes.
6. Transfer your frosting to a piping bag and using a tip of your choice, pipe your frosting onto your filled cupcakes. You can also use an ice cream or cookie scoop if you don’t have a piping bag.
7. For some fun finishing touches, add sprinkles and top with a cut rosemary sprig to give the appearance of a Christmas tree.