Begin by boiling water in a kettle. Preheat oven to 350 degrees. In a bowl, combine the flour, salt, sugar, cocoa powder, baking powder and soda, cinnamon, and espresso. Mix through to combine evenly by hand or on your stand mixer with the paddle attachment. To dry ingredients add the buttermilk, grapeseed oil, eggs, vanilla, and slowly mix in until fully combined. On slow continuous speed with a mixer, slowly add the boiled water. Careful that the speed is low, or you’ll be shooting boiling hot water around you and the kitchen. Equally divide the batter between two 9” round cake pans lined in parchment on the bottom. Bake 30-35 minutes or until your cake tester comes out clean. Let cool 15 minutes. Run a paring knife around the diameter of the cake and gently flip out on to a cake rack to cool. Ice the top layer of one, stack, ice the second top layer and all around the sides. Don’t resist… pour a glass of milk and have at it!
Put the chocolate in a heatproof bowl set over a simmering saucepan of water (do not let the bottom of the bowl touch the water) and stir occasionally until the chocolate is completely melted. Set the chocolate aside to cool to room temperature.
In the bowl of a stand mixer, fitted with the paddle attachment (or in a medium mixing bowl, using a handheld mixer), beat the butter on medium speed until smooth and creamy. Add the milk, mixing until completely blended. Add the cooled chocolate and mix until completely incorporated, 2 to 3 minutes, scraping down the sides of the bowl with a rubber spatula as necessary. Add the vanilla and beat just until mixed. With the mixer on low speed, gradually add 2 ½ cups confectioners’ sugar and continue beating, adding more sugar as needed, until you reach a creamy, silky frosting consistency. The frosting can be stored in an airtight container at room temperature for up to 2 days.