Start by making the caramel sauce because it needs two hours to cool and thicken.
To a medium sized pot melt butter over medium heat.
Add heavy whipping cream, whisk until combined.
Add brown sugar, whisk and allow the mixture to reach a boil.
Right when it reaches a rolling boil set a time for 2 1/2 minutes.
Stir every 30 seconds. Pull it off the heat. Whisk in the vanilla and flaky sea salt.
Let the pot sit at room temperature for two hours to thicken. Stir occasionally.
For the cake preheat oven to 350 degrees.
To a large mixing bowl or stand mixer bowl sift together flour, baking powder, baking soda, cocoa powder and salt.
Add sugar to the bowl and stir until combined.
To the bowl add buttermilk, oil, eggs and vanilla. Hand stir until everything is moistened or you end up with a very messy counter. Mix on low until everying is well combined. Scrape the bottom if needed.
With the mixer on low, very slowly add the coffee. Mix until fully combined
Pour batter in a prepared 9x13 dish or pan.
Bake uncovered for 35 minutes in the middle rack or until a toothpick comes out clean.
Using a toothpick, poke holes all over the surface of the cake.
Pour the thickened salted caramel sauce over top the warm cake and spread out. It will slowly seep into the holes.
Let the cake rest on the counter until it's room temperature for 2 hours.
For the whipped cream beat heavy whipping cream on high until soft peaks form. Add the powdered sugar and vanilla then continue whisking until firm peaks form.
Spread whipped cream evenly over the cake.
Top with Heath toffee bits and chill in the fridge for 2 hours.
Serve chilled.