Preheat oven to 300F. Spray the bottom and sides of a 6" round pan with pan spray. Line the bottom with parchment, pressing it in so that it's flat, and spray the parchment with pan spray. Doing this will aid in an easy release.

Set up a Bain Marie by bringing a pot of water to steaming and having ready a stainless steel bowl that can sit in the steaming water. A double boiler system will work here as well. Just make sure the water is not boiling.

In the stainless steel bowl add the chocolate and butter and set it in the Bain Marie. Gently melt the butter and chocolate stirring occasionally. Remove from Bain Marie when the chocolate mixture is melted, smooth and shiny and stir in the sea salt. Set aside.

Place the eggs and sugar in a stand mixer bowl and place it in the Bain Marie using the whisk to mix the sugar and eggs together until the mixture is warm to the touch. Immediately place on stand mixer fitted with whisk attachment and beat the mixture on medium speed until the eggs double in volume, about 5 minutes. The eggs will be thick and frothy.

Fold 1/3 of the egg mixture into the chocolate mixture. Then fold all of the chocolate mixture into the remaining egg mixture. Gently fold until no streaks are visible.

Pour into the 6" prepared cake pan and tap the pan firmly, flat on the counter at least three times to release any air bubbles.

Bake for 28-30 minutes on the center rack until it is almost baked yet still sticky to the touch.

Cool the cake in the pan on a wire rack. Cover when cool and refrigerate the cake in the pan overnight.

To release the cake hold the pan over a low flame, moving the pan around, on a stovetop for short periods of time (5-10 seconds), carefully checking several times to see if it will release when gently inverted. Do this several times. Alternatively, a shallow sink full of hot water will warm the bottom of the pan as well, again, for very short periods of time. If heated for too long, the cake will melt. Be sure to dry the bottom of the pan each time you invert the cake. Place the cake on a cake stand and cover until ready to top with ganache.

Pull the cake out of the fridge so it has time to come to room temperature before pouring the ganache on.

Place finely chopped couverture in a heat-proof bowl. Pour the heavy whipping cream into a 2-quart saucepan, add the sea salt and bring the cream to a scald, where just the edges of the milk are bubbling. Remove the cream from the heat and pour the cream all over and onto the couverture. Let the mixture set 2 minutes. Using a spoon or silicon spatula, slowly stir the mixture until a smooth emulsion is formed. Once all the chocolate is melted, add the butter, 1 tsp at a time, stirring gently to fully incorporate the butter. You'll notice the ganache is shiny and starting to thicken. Stir in the vanilla extract.

Allow the ganache to set at room temperature to thicken. The rate at which thickening will happen is dependent on the temperature of your kitchen. Mine took about 45 minutes to set up. Gently stir the ganache occasionally so that it cools evenly and throughly. You're aiming for a thick yet pourable, spreadable ganache. Keep your eye on it and have your cake on standby.

Once the ganache is to the desired consistency, it's time to pour it on the cake. *If you find the ganache is too thick to pour, gently reheat it in the Bain Marie. It will reheat quickly, so just a quick dip in and then out! Just make sure the Bain Marie water is not boiling. Use an offset spatula to work the ganache over the top of the cake. Start in the middle and work your way out. It will start to thicken quickly now, so work fast. You may have some ganache left over. If so, use it to make a few truffles once it becomes thick enough to roll... and it will, with a bit of time.

If finishing with chocolate shavings, use a vegetable peeler to make curls.

Serve at room temperature to get the most luxurious mouth feel!