Preheat oven to 350°F.

Grease or spray (3) 9” round baking pans. Line the bottom of each pan with parchment paper.

Using a medium bowl, whisk together cocoa powder and boiling water until smooth; set aside.

Using a large bowl, add flour, sugar, brown sugar, baking powder, baking soda and salt; whisk until well combined.

Add eggs, egg yolks, vegetable oil, sour cream and vanilla; whisk until well combined.

Finally, add the cocoa powder and hot water mixture to the bowl in several additions, whisking well between each addition.

Divide batter evenly into baking pans; tap pans lightly on countertop to release any air bubbles.

Bake at 350°F for 25-27 minutes, or until a toothpick inserted into center of cake comes out clean.

Let cakes cool in pan for 15 minutes and then transfer to a cooling rack until completely cool. (Note: Remove parchment paper from bottom of cakes when transferring them to the cooling rack.)

Using a countertop mixer, beat butter on medium speed until light and fluffy (~3 minutes).

Add vanilla extract, milk and powdered sugar 1 cup at a time, mixing on low speed after each addition.

Add salt, peppermint extract and several drops of green gel food coloring (start with just a couple drops and add more as needed); mix until well combined. (Note: If you desire a looser frosting, add an additional ½ Tbsp milk. For a thicker frosting, add an additional ½ cup of powdered sugar.)

Stir in ¾ cup mini chocolate chips. (The remaining chocolate chips will be used to garnish top of cake.)

Place one layer of cake on large platter. Spread ~¾ cup of frosting on top. Repeat with 2nd and 3rd layers of cake. Use remaining frosting on top and sides of cake.

Garnish top of cake with remaining mini chocolate chips.