Preheat your oven to 350°F (175°C) and grease two 9-inch round cake pans. In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. In a separate large mixing bowl, cream softened unsalted butter and granulated sugar until light and fluffy. Add room temperature eggs one at a time, mixing well; then stir in the instant coffee diluted in hot water and vanilla extract. Alternately fold in the dry ingredients and buttermilk until smooth.

Pour the cake batter evenly into the prepared pans and spread it out smoothly. Bake in the preheated oven for 27-31 minutes until the edges are lightly golden and a toothpick inserted into the center comes out clean. Once baked, remove from the oven and allow the cakes to cool in the pans for about 10 minutes before transferring them to wire racks to cool completely.

While the cake layers cool, make the luscious coffee buttercream. In a large mixing bowl, beat softened unsalted butter with a pinch of salt until light and fluffy. Gradually sift in powdered sugar, continuing to mix until combined. Add the remaining instant coffee and vanilla extract, mixing well until the buttercream is smooth, creamy, and spreadable. Set aside to firm up slightly if needed.

To prepare the coffee ganache, start by heating heavy cream over medium heat until just simmering, then whisk in more instant coffee until fully dissolved. In a heatproof bowl, combine the chopped white chocolate. Pour the hot coffee cream over the chocolate and let it sit for a minute; then stir the mixture over a double boiler until it's completely melted and smooth. Set aside to cool slightly, as this will help it thicken.

Once the cake layers are thoroughly cool, place one layer on a serving plate. Spread a generous amount of coffee buttercream on top, smoothing it evenly. Gently place the second layer on top of the frosted first layer. Chill the cake for about 15 minutes to set the buttercream before applying a crumb coat all over the cake.

After the crumb coat has set, apply a final layer of coffee buttercream evenly over the entire cake using a spatula. Smooth out the edges and top, creating a beautiful finish. Chill the frosted cake in the refrigerator for about 30 minutes to firm up the buttercream before adding the ganache.

Carefully drizzle the cooled coffee ganache over the edges of the cake, allowing it to drip down the sides. Use a spatula to smooth any ganache over the top of the cake for a seamless look. Return the cake to the fridge for an additional 15 minutes to let the ganache set properly.

Finally, pipe decorative swirls of the remaining coffee buttercream around the top edge of the cake. Garnish with espresso beans and a light dusting of cocoa powder for an elegant touch. Your stunning Cappuccino Cake is now ready to be served and enjoyed!