Preheat your oven to 350°F. Lightly grease an 8-inch round, 3-inch-deep light-colored cake pan or springform pan with nonstick cooking spray. Place a parchment round on the bottom of the pan and spray it again.
In a large microwave-safe bowl, heat the chocolate chips and butter in 30-second intervals, stirring between each, until just melted. Stir until smooth. Whisk in the sugar, espresso powder, salt, and vanilla extract. Let the mixture cool slightly.
1 ¼ cups semisweet chocolate chips, 1 1/2 stick unsalted butter, 3/4 cup granulated sugar, 1 teaspoon instant espresso powder, 1/4 teaspoon fine salt, 1 teaspoon vanilla extract
Add the eggs all at once, whisking vigorously until smooth. Whisk in the cocoa powder until just combined. The batter will be thick.
4 large eggs, 1/2 cup Dutch-process unsweetened cocoa
Pour the batter into the prepared pan and smooth the top. Bake for 25–30 minutes, or until the edges are set, the center is slightly wobbly, and an instant-read thermometer inserted in the center reads at least 200°F.
Remove the cake from the oven and let it cool in the pan on a wire rack for 10 minutes. The cake will deflate slightly as it cools. Use a thin, flexible knife or offset spatula to loosen the edges while the cake is still warm, making it easier to unmold later. Let it cool completely in the pan.
Chocolate shavings, fresh raspberries and/or strawberries for garnish, Whipped cream