To make the ganache, put the white chocolate in a medium bowl; set aside. In a small bowl, stir together the gelatin and 2 tablespoons water; set aside. In a medium saucepan over medium, combine the cream, mascarpone and honey.

Cook, stirring often, until the mascarpone is fully melted and the mixture begins to bubble at the edges, 6 to 8 minutes.

Remove from the heat, add the gelatin mixture and whisk until completely dissolved. Immediately pour the cream mixture over the white chocolate, then let stand for about 1 minute.

Whisk the chocolate mixture until completely smooth. Press plastic wrap directly against the surface and cool to room temperature, then refrigerate until well chilled and fully set, at least 4 hours or up to 24 hours.

To make the cake, heat the oven to 350°F with a rack in the middle position. Mist the bottom and sides of a 9-by-2-inch round cake pan with cooking spray, line the bottom with a round of kitchen parchment, then mist the parchment.

Using a paper towel, evenly spread the oil. Dust the pan evenly with cocoa and knock out any excess.

In a large bowl, whisk together the cocoa, flour, sugar, baking powder, baking soda and salt. In a medium bowl, whisk the eggs, buttermilk, oil and vanilla until homogeneous.

Add the liquid ingredients to the dry ingredients, and, using a large silicone spatula, fold until the batter is completely smooth.

Pour the batter into the prepared pan, then rap the pan 4 or 5 times against the counter to release any large air bubbles. Bake until a toothpick inserted at the center of the cake comes out clean, about 45 minutes.

Cool in the pan on a wire rack for about 20 minutes. Run a paring knife around the edge of the cake to loosen, then invert it onto the rack and lift off the pan.

Remove and discard the parchment, then carefully re-invert the cake and let cool completely. Wrap the cake in plastic wrap and set on a large, flat plate. Refrigerate for at least 4 hours or up to 24 hours.

When ready to assemble, make the soaking syrup. In a 1-cup liquid measuring cup or small microwave-safe bowl, stir together the sugar and ¼ cup water.

Microwave on high for 30 seconds, then stir until the sugar is fully melted and the syrup is clear. Add the instant espresso and whisk until dissolved. Cool to room temperature.