Chop the semi-sweet chocolate into pieces and heat the cream until it just starts to boil. Pour the hot cream over the chocolate and let it sit for 2 minutes before whisking to create a smooth ganache. Place the ganache in the freezer to firm up.

In a separate bowl, mix together the salt and flour.

Set up a double boiler and bring the water to a simmer. Add the dark chocolate and butter to the bowl and let them melt together, then remove from heat.

In another bowl, whisk the eggs, egg yolks, and sugar together. Make sure the melted chocolate mixture has cooled slightly before combining it with the egg mixture.

Fold the chocolate-egg mixture into the flour mixture and stir until you have a smooth batter.

Prepare six ramekins by buttering them well to prevent sticking. Optionally, you can dust the insides with cocoa powder or turbinado sugar by adding a bit of sugar, tilting the ramekin, and spinning it to coat the sides.

Pour the cake batter into each ramekin until they are half full.

Take a scoop of the frozen chocolate ganache and place it in the center of each ramekin. Then, fill the ramekins to the top with more cake batter and gently tap them to settle the mixture.

Bake the ramekins in a preheated oven at 425°F for about 12 minutes, until the edges are set but the centers remain soft and gooey.

Once baked, remove them from the oven and place a plate on top of each ramekin. Carefully invert them to release the cakes.

Dust the tops of the cakes with powdered sugar and serve with a generous scoop of ice cream.