Combine sugar, cornstarch, and water in a saucepan over medium heat, stirring until the mixture is wet and sugar starts to melt. Add raspberries, stir to coat, cook until raspberries soften and release juice, then strain and refrigerate.

Preheat oven to 350°F. Prepare three 8-inch cake pans with baking spray and parchment paper. Mix dry ingredients: flour, sugar, cocoa, baking soda, baking powder, and salt.

In a separate bowl, mix wet ingredients: milk, oil, vanilla, and eggs. Combine wet and dry ingredients, then add hot water gradually, mixing until smooth.

Divide batter among pans and bake for 22-25 minutes. Cool the cakes on a wire rack.

Prepare frosting by creaming butter, adding melted chocolate in batches, then mixing in cocoa powder, powdered sugar, and heavy cream to desired consistency.

Make ganache by pouring hot cream over chocolate chips, whisk until smooth. Level cake layers, layer with raspberry filling, and cover with frosting and ganache. Decorate as desired.