Preheat oven to 350 degrees. Grease two 8 or 9 inch round baking pans and optionally line them with parchment or wax paper.

Stir together sugar, flour, cocoa, baking powder, baking soda, and salt in a large bowl.

Add eggs, vanilla, oil, and buttermilk to the dry ingredients. Beat for 2 minutes.

Stir in boiling water until the batter is thin. Pour the batter into the prepared cake pans.

Bake for 30-35 minutes or until a toothpick inserted into the center comes out clean. Cool for 10 minutes, then run a knife around the edges to loosen the cake. Invert cakes onto cooling racks.

For raspberry filling, combine sugar, water, lemon juice, and cornstarch in a medium saucepan over medium heat. Stir to combine and then add raspberries. Cook until raspberries soften and sauce thickens. Cool completely before filling the cake.

For chocolate frosting, combine melted butter and cocoa powder. Add powdered sugar, milk, and vanilla extract. Beat until smooth and creamy, adjusting with more powdered sugar or milk as needed.

To assemble, place one cake layer on a plate, add desired raspberry filling, and smooth it out. Top with the second cake layer. Frost the outside with chocolate frosting and add fresh raspberries on top if desired.