Preheat the oven to 350º F, and position a rack in the lower third of the oven.
Line 2 6” round cake pans (with 2” sides) with parchment paper circles on the bottom, and lightly grease the sides of the pan with oil.
Next, in a medium bowl, whisk together the flour, cocoa powder, and baking soda. Set aside.
In a small bowl, whisk together the melted butter, sour cream, eggs, vanilla and coffee.
Combine the wet and dry ingredients, mixing just until combined.
Divide the mixture between the cake pans, and bake for 29-32 minutes, or until a toothpick inserted in the cake comes out clean. If you under-bake the cake, it will sink, so make sure to check in! It will also start to pull away from the sides of the pan when it’s done.
Let the cakes cool for 15 minutes in the pan, run a knife around the edge, and carefully tilt the cakes out of their pans. Let cool on a wire rack.
Meanwhile, make the buttercream by beating the butter until light and fluffy, about 1 minute. Next, continue beating while adding the powdered sugar 1 cup at a time. When all of the powdered sugar is incorporated, add half of the cream, and beat until combined. Finally, add the cocoa powder, remaining cream and vanilla extract. Beat until light and fluffy. Add additional heavy cream if the mixture isn’t soft and spreadable.
The easiest way to frost a cake is to have all of the buttercream in a piping bag. It’s not entirely necessary, but it’s considerably more effort without one. So, scrape all of the frosting into a large piping bag fitted with a 1” open tip.
Place one of the cake layers on a cake stand. Spread the strawberry jam over the surface.
Pipe some of the buttercream frosting in a single layer on top.
Place the other cake layer on top, and then pipe frosting all over the top and sides of the cake. Using a bench scraper or cake icing smoother, press all of the frosting into a smooth layer. Take your time!
Place the cake in the fridge for an hour.
Meanwhile, make the chocolate drip: heat the heavy cream in a small bowl in the microwave until steaming, about 20 seconds. Add the 1/3 cup of chocolate, and without stirring, cover the bowl and let it rest for 5 minutes.
After 5 minutes, remove the plate and slowly whisk the chocolate and cream mixture until it comes together into a smooth melted chocolate mixture.
Remove the cake from the fridge. Carefully spoon the melted chocolate mixture around the edges of the cake, gently nudging it to drip over the sides.
Place the strawberries around the edges of the cake, and serve!