This is a really great "just because" cake that's easy to make but still looks and tastes amazing enough for a special occasion. A beautifully moist chocolate cake is spiked with instant espresso powder and bathed in a coffee-flavored ganache. If you want to make the recipe even simpler, serve the glaze warm alongside wedges and let guests spoon it over their own slice.
Preheat the oven to 350 degrees F. Coat a 9-inch springform pan with nonstick spray. Line the base and sides with parchment paper.
For the cake: Cream the butter and brown sugar together in the bowl of an electric stand mixer fitted with the paddle attachment until light and fluffy, 3 to 4 minutes. Add the eggs one at a time, mixing until fully incorporated before adding the next and scraping the sides of the bowl after each addition. Mix in the vanilla.
Whisk the flour, cocoa powder, espresso powder, baking powder and salt in a medium bowl to combine. Add about half of the flour mixture to the mixer bowl and mix to combine. Scrape the bowl well, then add the buttermilk and mix on low speed to combine. Add the remaining flour mixture and mix on low speed to incorporate.
Scrape the batter into the prepared cake pan and spread into an even layer. Bake until a toothpick inserted into the center comes out clean, 25 to 30 minutes.
Cool the cake for 10 minutes in the pan, then unlock and remove the sides of the pan and remove the parchment strips. Cool the cake completely on a cooling rack placed over a parchment-lined baking sheet.
For the glaze: Put the chocolate and espresso powder in a medium bowl. Heat the cream to a simmer in a small saucepan over medium heat, then pour the cream over the chocolate. Let sit for 30 seconds, then stir until the mixture is smooth. Transfer to a measuring cup with a pour spout.
Start by pouring glaze around the edges of the cake, then continue pouring and working towards the center of the cake until it is covered. Let the glaze set for 5 minutes, then gently transfer to a serving platter or cake stand (do not let the glaze set fully on the cooling rack). Once the glaze is set, the cake is ready to serve.