Preheat the oven to 350ºF. Grease and flour three 9-inch cake pans. Set aside.

In a large bowl, whisk together the flour, sugar, baking soda, salt and cocoa powder. In a large glass measuring cup, whisk together the hot water, oil, vinegar and vanilla extract. Slowly whisk the water mixture into the flour mixture until thoroughly combined and smooth, about 1 minute. Divide the cake batter evenly between the prepared cake pans.

Bake for 15-20 minutes, or until a toothpick inserted in the center comes out clean. Let cool in the pans for about 10 minutes, then gently run a knife around the edges and invert onto a wire rack. Let cool completely.

Place the thawed berries in a fine mesh sieve over a glass measuring cup. Press the juice out of the berries with a spoon or rubber spatula, set aside. Add enough water to equal ¾ cup. Pour the liquid into a small saucepan, whisk in the sugar and cornstarch and bring to a simmer over medium-high heat, whisking occasionally until thickened, about 5 minutes. Remove from heat and stir in the lemon juice and reserved berries. Chill completely in the refrigerator.

Place chopped chocolate in a heatproof bowl. Pour cream into a small saucepan, place over medium heat and bring to a simmer. Immediately pour over chocolate and let sit for 2 minutes. Whisk until completely smooth and melted, then whisk in the butter, 1 tablespoon at a time until smooth. Refrigerate ganache, whisking occasionally until thick, about 30 minutes. Reserve ½ cup of ganache in a small bowl for decorating.

Place frozen raspberries in a small saucepan over medium heat and stir often. Once thawed, press through a fine mesh sieve. Pour in enough heavy cream to measure 1 cup. In a food processor, combine butter, confectioners' sugar and heavy cream/berry mixture; process for 5 minutes until smooth and shiny. Transfer to a stand mixer and beat on medium-high for 20 minutes until fluffy.

Place one cooled cake layer on a board. Spread half of the ganache in an even layer, pipe a border around the perimeter, and spread half of the raspberry filling. Top with another layer of cake and repeat, finishing with the last cake layer.

Frost the top and sides of the assembled cake with raspberry buttercream, smoothing the surface. Chill for at least 30 minutes.

Make the chocolate glaze by heating cream and pouring over chocolate. Let sit for 2 minutes, whisk until smooth. Whisk in corn syrup and vanilla extract. Let cool for 10 minutes, then pour over the cake to cover.

Transfer the remaining ganache to a pastry bag and pipe swirls on top. Garnish with sprinkles and fresh raspberries if desired. Chill until ready to serve.