Preheat your oven to 350°F/175°C. Line and grease 2 x 8 inch cake pans
Whisk together the flour, salt, cocoa powder, baking powder, and baking soda until smooth.
In a stand mixer with the paddle attachment, beat the butter and the light brown sugar together on medium speed until light and fluffy. This takes about 5 minutes. Scrape down the bowl every few minutes.
Add the eggs one at a time, beating well after each addition. Add the vanilla and beat well.
Reduce the speed to low. Add the dry ingredients and buttermilk in three additions, starting and ending with dry.
Pour in the melted chocolate and mix until smooth.
Divide the batter evenly between the two pans (about 620 grams per pan).
Bake for 25-28 minutes. A toothpick inserted will come out clean.
Let cool completely.
Place your chopped chocolate in a heatproof bowl. Set aside.
Take a small saucepan and place it on your stove over medium heat. Add the sugar ¼ cup at a time, letting the sugar dissolve completely until you add the next ¼ cup.
Stir occasionally until the sugar has completely dissolved and turns a dark amber colour. Turn the heat off.
Add the butter in a piece at a time, be careful as it may sputter! Stir with a heatproof spatula as you add the butter. Stir in the cream, salt, and vanilla.
Pour half of your caramel sauce over the chocolate. Use a rubber spatula to whisk until smooth. Leave to cool and thicken. Keep the rest of the salted caramel in a container and allow to cool.
Chill your mixing bowl for at least an hour or overnight.
In a stand mixer with the paddle attachment, beat together the heavy cream, salt, sugar, and vanilla at a low speed. The sugar should dissolve after 2 minutes.
Increase the speed to high for 2 minutes until the mixture resembles Greek yogurt.
With the mixer on low speed, add the cream cheese a tablespoon at a time. Once all the cream cheese is in, stop the mixer. It should look like cottage cheese. Scrape the bowl then turn the speed to high and beat for 3 minutes. It should look smooth and fluffy. Pour in your cocoa powder, and mix for 1 minute.