NOTES :
The cake batter will be very thin after adding the boiling water .
To make ahead , let the baked cake layers cool completely . Wrap them well with plastic wrap and then with foil . Put each layer into a freezer bag and freeze up to 2 months . To serve , thaw in the refrigerator overnight with wrapping intact . The next day , the layers will be ready to fill and frost .
Preheat oven to 350 degrees . Prepare two 9-inch cake pans by spraying with baking spray or buttering and lightly flouring .
Add flour , sugar , cocoa , baking powder , baking soda , salt , and espresso powder to a large bowl or the bowl of a stand mixer . Whisk through to combine or , using your paddle attachment , stir through flour mixture until combined well .
Add milk , oil , eggs , and vanilla to flour mixture and mix together on medium speed until well combined . Reduce speed and carefully add boiling water to the cake batter until well combined .
Distribute cake batter evenly between the two prepared cake pans . Bake for 30 – 35 minutes , until a toothpick or cake tester inserted in the center of the chocolate cake comes out clean .
Remove from the oven and allow to cool for about 10 minutes . Remove from the pan and cool completely .
Frost cake with Chocolate Buttercream Frosting .