Step 1: Preheat the Oven - Preheat your oven to 350°F (175°C).
Step 2: Prepare the Cupcake Batter - In a large bowl, whisk together the cocoa powder and baking soda. Stir in the boiling water until combined.
Step 3: Mix Wet Ingredients - Add the melted butter, vegetable oil, granulated sugar, vanilla extract, and salt. Mix well, then add eggs and yolks, beating until fluffy.
Step 4: Incorporate Dry Ingredients - Gradually sift in the flour and evaporated milk, mixing until just combined.
Step 5: Fill the Muffin Tin - Line your muffin tin with cupcake liners and fill each cup two-thirds full with batter.
Step 6: Bake - Bake for 18-20 minutes, or until a toothpick comes out clean. Cool in the tin for 5 minutes, then transfer to a wire rack.
Step 7: Make the Chocolate Buttercream Frosting - Beat softened butter until creamy, then add cocoa powder and powdered sugar, alternating with milk and vanilla until desired consistency.
Step 8: Frost the Cupcakes - Once the cupcakes are cool, use a piping bag to frost them. Garnish with chocolate shavings or sprinkles if desired.
