In a medium saucepan, combine cornstarch, water, sugar, and lemon juice with raspberries. Stir over medium heat until boiling, then cook for 5 minutes until thickened. Allow to cool.

Preheat the oven to 350°F (177°C) and prepare three 9-inch round cake pans.

In a large bowl, whisk together flour, cocoa powder, sugar, baking powder, baking soda, salt, and espresso powder until no lumps remain.

In a separate bowl, mix oil, eggs, sour cream, buttermilk, and vanilla until smooth using an electric mixer.

Gradually add dry ingredients to the wet mixture, stirring gently. Pour in hot coffee or water and blend until smooth.

Gently fold in raspberries coated with flour.

Divide batter among prepared pans and bake for 24-26 minutes or until a toothpick comes out clean.

Cool cakes in pans for 10 minutes, then transfer to wire racks to cool completely.

Prepare buttercream by beating butter until creamy, then gradually adding powdered sugar, cocoa powder, cream, salt, and vanilla until smooth.

Layer the cakes with buttercream and raspberry filling, crumb coat with buttercream and chill.

Prepare ganache by heating cream to boiling, pouring over chocolate chips to melt, then pour over the cake and chill until set.