Preheat your oven to 350 degrees Fahrenheit. Line 24 wells of a muffin pan with paper cupcake liners and set aside.
In a medium mixing bowl, whisk together the cocoa powder, baking soda, and salt. Carefully add the boiling water and whisk until well blended. Set the mixture aside.
In a large mixing bowl, combine the granulated sugar, melted butter, vegetable oil, and vanilla.
Using an electric mixer or a whisk, beat in the eggs and egg yolks just until combined.
Then beat in the cocoa mixture and the milk until just combined.
Sift in the flour and stir the batter with a wooden spoon or spatula until the flour is just incorporated.
Scoop the batter into the prepared muffin pans, filling each well to about 2/3 full.
Bake the cupcakes for 18-20 minutes until a toothpick inserted into the center comes out clean.
Cool the cupcakes in the pan for 5 minutes, then transfer to a wire cooling rack to cool completely to room temperature.