Make a chocolate cake according to the description on the box. I recommend making (2) 8in cake layers.

Sift the powdered sugar and cocoa powder into a large bowl. This is very important or your frosting will turn out lumpy.

In a medium saucepan on medium to low heat, add 4 tablespoons of the butter, the brown sugar, and a half cup of the heavy cream. Heat for 8 minutes stirring frequently.

Reduce heat to low and cook another 10 minutes, stirring frequently. The mixture should thicken and become a deep golden brown.

Take the saucepan off the stove and do the following: Add the remaining 4 tablespoons of butter and stir. Break the chocolate into pieces and stir until combined. Add the remaining half cup of heavy cream and the 1 tsp vanilla. Stir until everything is combined.

Pour the saucepan into the large bowl of powdered sugar and cocoa powder. Using a whisk, whisk everything together until smooth.

Leave to cool at room temperature, whisking occassionally. It will more than likely still be a little runny and hard to keep it on the cake. I recommend refrigerating until it is the right consistency. You want it to be spreadable but not run. If you leave it in the refrigerator too long and it gets too thick to spread on your cake, let it sit on the counter a few minutes to warm back up.

Place one 8in cake layer on a board or your cake carrier and spoon or pipe a thick layer of frosting. Spread it out to cover the top of the cake. I recommend putting this layer of cake in the refrigerator for 10 minutes to thicken the icing especially if it's warm in the kitchen. This ensures it sets up and won't push out when you put the top layer on and frost the rest of the cake.

Add the other layer of cake onto the frosted bottom layer. Frost the whole cake and decorate as desired. Serve immediately or refrigerate until serving.