1-First Step: Prepare and preheat Preheat your oven to 350°F (177°C). Grease a 6-inch cake pan and line the bottom with a parchment round for easy release. If you have a springform pan, use the same method. Set a rack in the center of the oven so the cake browns evenly.

2-Second Step: Dry ingredients In a medium bowl, sift together 1/2 cup (63g) all-purpose flour, 1/4 cup (21g) unsweetened cocoa powder, 1/4 teaspoon baking soda, 1/2 teaspoon espresso powder (optional), and 1/4 teaspoon salt. Sifting reduces lumps and helps the dry ingredients mix more evenly with the wet ingredients.

3-Third Step: Wet ingredients In a separate bowl, whisk 1/4 cup (60ml) vegetable oil with 1/2 cup (100g) granulated sugar until combined. Add 1 large egg at room temperature, 1/2 teaspoon pure vanilla extract, and whisk until the mixture becomes lighter in color and slightly thickened. This step helps incorporate air for a tender crumb.

4-Fourth Step: Combine and add buttermilk Add the dry ingredients to the wet ingredients in two parts, alternating with 1/4 cup (60ml) buttermilk at room temperature. Start and finish with the dry mix. Stir gently until just combined; do not overmix or the cake will be dense. A few streaks of flour are fine mixing will finish them.

5-Fifth Step: Transfer to pan and bake Scrape the batter into the prepared 6-inch pan and smooth the top with a spatula. Bake at 350°F (177°C) for 27 to 30 minutes. Begin checking at 27 minutes by inserting a toothpick into the center; it should come out clean or with a few moist crumbs. Oven temperatures vary; if using a dark pan or if your oven runs hot, check a minute or two earlier.

6-Sixth Step: Cool and unmold Let the cake cool in the pan for 10 minutes on a wire rack. Run a small knife around the edge if needed, then invert onto the rack and remove the parchment. Let cool completely before adding ganache so the topping sets glossy.

7-Final Step: Make the ganache and finish Place one 4-ounce (113g) semi-sweet or bittersweet chocolate bar, finely chopped, in a heatproof bowl. Heat 1/2 cup (120ml) heavy cream in a small saucepan over medium heat until it just begins to simmer; do not boil. Pour the hot cream over the chopped chocolate and let sit for 1 minute, then stir until smooth. If the chocolate has not melted fully, gently heat the mixture in 10 second bursts in the microwave, stirring between pulses. Pour the ganache over the cooled cake, letting it drip down the sides for a pretty finish. Decorate with optional garnishes such as raspberries, mint, or sprinkles for contrast. Chill for 10 to 20 minutes to set the ganache, then slice and serve.