• Prep the pans and oven - Preheat the oven to 325°F / 165°C. Grease and line one 9-inch round cake pan (or two 7-inch round cake pans) with parchment on the base and strips up the sides. Mud cakes are moist and delicate, so the parchment makes unmolding easy and keeps the sides neat.
• Melt the chocolate and butter - In a microwave-safe bowl, melt the butter and chocolate together until smooth and glossy. You can do this over low heat on the stovetop or in short bursts in the microwave. Stir well and remove from the heat.
  226 g Unsalted butter , 226 g Chocolate
• Add the sugars - Stir the white sugar and brown sugar into the warm chocolate mixture. Mix until the batter looks glossy and the sugars start to dissolve (it won’t become perfectly smooth—and that’s fine).
  200 g White sugar, 220 g Brown sugar
• Add the eggs - Add the eggs one at a time, mixing well after each addition. This helps the batter emulsify so it bakes evenly and doesn’t split.
  3 large Eggs
• Add sour cream and vanilla - Stir until smooth. At this stage the batter should look thick, shiny, and cohesive.
  120 ml Sour cream, 2 tsp Vanilla extract
• Sift in the dry ingredients - Sift the flour, cocoa powder, baking powder, baking soda, and salt directly into the bowl. Fold just until the flour disappears. Don’t overmix here—once the flour is in, you want to keep the crumb tender.
  225 g All-purpose flour, 50 g Cocoa Powder, 1 tsp Baking powder, ½ tsp Baking soda, 1 tsp Salt
• Add the hot coffee last - Pour in the hot water mixed with instant coffee and stir until the batter is smooth and uniform. The batter will loosen up and look more fluid—that’s exactly what you want for a mud cake.
  250 ml Boiling water
• Bake - Pour the batter into the prepared pan and bake for 80 to 90 minutes until a skewer comes out with moist crumbs (not wet batter). Don’t overbake—mud cake is meant to be fudgy and moist. (If you bake in two 7-inch cake pans, they will take about 35 to 40 minutes.
• Cool completely - Let the cakes cool in the pans for about 10–15 minutes, then turn them out onto a rack to cool completely before frosting. For the cleanest layering, chill the cakes for 2 hours before assembling.

Assemble

• Make the ganache - Heat the cream until it’s very hot but not boiling. Pour it over the chopped chocolate and let it sit for a couple of minutes, then stir until smooth. Add the butter and corn syrup and stir until glossy.
  400 g Dark chocolate , 320 ml Heavy cream, 2 tbsp Unsalted Butter, 2 tbsp Corn syrup or honey
• Cool to spreading consistency - Let the ganache sit at room temperature until it thickens to a soft, spreadable consistency. If your kitchen is warm, pop it in the fridge briefly and stir every few minutes so it thickens evenly.
• Assemble - Place one cake layer on a board or plate. Spread an even layer of ganache over the top, add the second layer, then cover the top and sides with the remaining ganache. Chill briefly if needed, then finish smoothing.