Preheat the oven to 350°F (175°C). Grease an 8x4-inch loaf pan and line it with parchment paper for easy removal.
In a mixing bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.
In another bowl, whisk granulated sugar, brown sugar, eggs, vegetable oil, milk, vanilla extract, and hot coffee until smooth.
Gently fold the wet ingredients into the dry ingredients until just combined. Avoid overmixing to keep the cake light and fluffy.
In a small bowl, mix Nutella, softened cream cheese, and powdered sugar until smooth.
Pour half of the cake batter into the prepared loaf pan. Spoon the Nutella filling down the center, keeping it slightly away from the edges to prevent over-spreading.
Cover with the remaining batter, spreading it evenly. Bake for 45 to 55 minutes or until a toothpick inserted near the edge comes out clean.
Let the cake cool in the pan for 15 minutes before transferring it to a wire rack to cool completely.
For the ganache, heat the heavy cream until it simmers, then pour it over the chopped chocolate. Let it sit for 2 minutes before stirring in the butter until smooth and glossy.
Pour the ganache over the cooled loaf cake, allowing it to drip naturally down the sides.
Decorate with KitKat bars and optional chocolate curls while the ganache is still soft. Refrigerate for 20 minutes to set before slicing.