Preheat the oven to 350 degrees F (175 degrees C). Grease and line two 9-inch cake pans with parchment paper.

Beat sugar and butter for cake together in a bowl with an electric mixer until creamy; add eggs and beat until pale in color.

Mix 1 cup boiling water and cocoa powder together in a separate bowl. Mix into the sugar mixture. Combine baking soda with remaining boiling water and add to the batter. Mix in flour and baking powder until just combined. Pour evenly into the prepared pans.

Bake in the preheated oven until a toothpick inserted into the centers comes out clean, about 30 minutes. Cool for 15 minutes in the pans; run a knife around the edges of the cakes and transfer onto wire racks to cool completely.

While cakes cool, prepare filling. Combine chocolate chips, sugar, hot water, and coffee granules in a small saucepan. Stir over low heat until sugar is dissolved and mixture is smooth. Cool completely.

Whip cream until it starts to thicken; add cooled chocolate mixture and whip until stiff.

Split each cooled cake layer in two with a knife. Divide filling into 4 equal portions. Spread 1/4 of the filling on the first cake layer, top with another layer, and repeat until you've frosted the top layer. Chill at least 1 hour for best results.