Preheat oven to 350°F. Prepare 2 cupcake pans with cupcake liners.

In a large mixing bowl, add the flour, baking soda, baking powder, and salt. Whisk together to combine. Set aside.

In another large bowl, add eggs, sugar, sour cream, vegetable oil, and vanilla. Whisk together until smooth and well combined.

In a small mixing bowl or 2-cup liquid measuring cup, add the hot coffee and cocoa powder. Whisk together until well-combined and smooth. Allow to sit for 2 minutes.

Add the cocoa mixture into the mixing bowl with the wet ingredients, then mix until smooth.

Add the wet ingredients into the bowl with the dry ingredients, and mix until smooth.

Pour the cake batter into the prepared cupcake pans, filling 2/3 full, and bake for 20 minutes or until an inserted toothpick comes out clean. Allow to cool completely before frosting.

Add butter to a stand mixer fitted with the whisk attachment or a large bowl. Beat on high until butter is doubled in volume, about 3-5 minutes.

Turn the mixer to low and slowly add the confectioners sugar, cocoa powder, and salt. Beat on medium until completely incorporated and smooth.

Add in the heavy cream, corn syrup, and vanilla. Beat until well-combined, then add to a piping bag to pipe onto cupcakes.