Let’s create this stunning Strawberry Chocolate Cake! First, bake the chocolate cake layer. Preheat oven to 350°F (177°C). Grease a standard 9-inch round baking pan (NOT a springform pan for this step) and line the bottom with parchment paper. Set aside.

In a large bowl, stir together the dry cake ingredients: sugar, flour, cocoa powder, baking powder, baking soda, and salt. Whisk well to combine and remove lumps. Add the egg, milk, vegetable oil, and vanilla extract. Mix with an electric mixer on medium speed for 2 minutes until well combined. Carefully stir in the ½ cup of boiling water until just combined (the batter will be very thin).

Pour the thin batter into the prepared standard 9-inch pan. Bake for 25-35 minutes, or until a wooden toothpick inserted into the center comes out clean. Let the cake cool in the pan for 10 minutes. Then, carefully invert the cake onto a wire rack, peel off the parchment paper, and let it cool completely. Turning it upside down helps flatten any dome.  

While the cake cools, prepare the chocolate mousse filling. In a small dish, sprinkle the 2 teaspoons of unflavored gelatin over the 2.5 tablespoons of cool water. Let it sit undisturbed for 5-10 minutes to bloom (hydrate and solidify). Set aside.

In a medium heatproof bowl, combine the chopped semi-sweet chocolate, chopped white chocolate, and the 6 tablespoons of butter. Melt this mixture gently over a double boiler (a bowl set over simmering water, not touching) or in the microwave at 50% power in short bursts, stirring frequently, until completely melted and smooth. Set aside to cool until lukewarm but still fluid.

Gently heat the bloomed gelatin over very low heat (or microwave for 5-10 seconds) just until it liquefies completely – do not boil. Ensure there are no lumps. Let it cool slightly.

In a large (preferably chilled) bowl, combine the 1 3/4 cups of cold heavy whipping cream and the 1 1/2 teaspoons of vanilla extract. Using an electric mixer with whisk attachment(s), beat on medium-high speed until medium peaks start to form (peaks hold their shape but curl slightly at the tip). Gradually add the sifted powdered sugar while beating. Slowly drizzle in the cooled liquid gelatin while the mixer is running on medium speed. Continue beating until stiff peaks form. Be careful not to overbeat.

Now, combine the mousse components. Gently stir a few large spoonfuls (about 1 cup) of the whipped cream mixture into the cooled melted chocolate-butter mixture. This lightens the chocolate base, making it easier to fold. Add the lightened chocolate mixture back into the remaining whipped cream. Using a large rubber spatula, gently fold the chocolate mixture into the whipped cream, scraping from the bottom and turning the bowl, until just combined and no white streaks remain. Be careful not to deflate the airy mixture.

Time to assemble the cake! Place the completely cooled chocolate cake layer onto your final serving plate. Carefully place the ring (the sides only) from your 9-inch springform pan around the cake layer, ensuring it fits snugly against the plate. Spread a thin layer of the chocolate mousse (about ½ cup) evenly over the cake base inside the ring.

Prepare the strawberries: Hull them and cut the stem ends flat so they can stand upright. Select enough nice-looking berries, halve them vertically, and arrange them cut-side-out, tightly against the inside edge of the springform ring, standing upright on the thin mousse layer. Fill the entire center area inside the ring of halved berries with whole strawberries, standing them upright as well. Trim the bottoms of taller berries as needed so they are all roughly the same height and fit below the top of the ring.

To fill the gaps without disturbing the berries, the recipe suggests transferring the remaining mousse to a piping bag (or large Ziploc with corner snipped). Carefully pipe the mousse into all the gaps between the standing strawberries, ensuring there are no large air pockets. Pipe or gently spoon the rest of the mousse over the tops of the strawberries, spreading it carefully to create a smooth, level top surface even with the top of the springform ring.

Place the assembled cake (still in the ring on the serving plate) into the refrigerator for at least 4-6 hours, or preferably overnight, until the mousse is completely set and firm.

Once the mousse is set, make the ganache topping. Place the 5.5 oz of chopped semi-sweet chocolate in a heatproof bowl. Heat the 2/3 cup of heavy cream in a small saucepan just until it simmers. Pour the hot cream over the chopped chocolate. Let it sit for 2-3 minutes, then whisk gently until the ganache is completely smooth and glossy. Let it cool slightly until it’s barely warm but still easily pourable.

Pour the slightly cooled ganache over the set mousse layer inside the springform ring. Gently tilt the plate or use an offset spatula to spread it into an even layer covering the entire top. Place the cake back in the refrigerator for at least 30-60 minutes, or until the ganache is set.

Once the ganache is set, carefully run a thin, sharp knife or offset spatula around the inside edge of the springform ring to loosen it from the mousse. Gently unlatch and lift off the springform ring.

Optional: Make the chocolate curls just before serving. Melt the 3.5 oz of semi-sweet baking chocolate with the 1 tablespoon of shortening or oil until smooth. Spread this mixture in a thin, even layer onto the back of a cool metal baking sheet. Place the sheet flat in the freezer for 6-8 minutes, just until the chocolate is firm but not rock hard. Remove from freezer and let it sit at room temperature for about 2 minutes (timing depends on room temp). Hold a sturdy metal spatula or bench scraper at about a 45-degree angle to the chocolate. Push firmly across the chocolate surface; if the temperature is right, it should form curls. If it shatters, it’s too cold (wait another minute). If it mushes, it’s too soft (freeze briefly again). Gently lift curls onto the cake.

Garnish the top of the cake with the chocolate curls (if using) and fresh strawberries. Keep refrigerated until ready to serve