Instructions:
- Preheat oven to 350°F (175°C). Grease, flour, and line two 9-inch round cake pans with parchment rounds.
- Whisk together flour, sugar, cocoa powder, baking soda, baking powder, and salt in a large bowl.
- In a separate bowl, whisk together buttermilk, oil, eggs, and vanilla until just combined.
- Add the wet ingredients to the dry ingredients and beat on medium speed until just incorporated (do not overmix!).
- Carefully pour the hot coffee into the batter while mixing slowly on low speed until smooth. The batter will be very thin.
- Divide batter evenly between prepared pans. Bake for 30–35 minutes, or until a skewer comes out with moist crumbs attached. Cool layers in pans for 15 minutes, then invert onto a wire rack to cool completely.
- Prepare the custard: Toast pecans and coconut separately until fragrant; set aside.
- In a saucepan, melt butter, then whisk in sugar until smooth. Bring to a gentle simmer over medium heat.
- Temper the yolks: Slowly drizzle about half a cup of the hot butter mixture into the egg yolks while whisking constantly. Pour the tempered yolk mixture back into the saucepan.
- Add evaporated milk and salt. Cook over medium-low heat, stirring constantly with a rubber spatula, until the mixture thickens enough to coat the back of the spoon (do not boil!).
- Remove from heat. Stir in vanilla, toasted pecans, and toasted coconut. Allow the frosting to cool completely until thick and spreadable (about 45 minutes).
- Assemble the cake: Place one cooled layer on a serving plate. Spread half of the cooled custard filling evenly over the top. Top with the second layer.
- Use remaining frosting to cover the top and sides lightly. Refrigerate for at least 1 hour before slicing to allow the custard to set firmly.