Prepare a double boiler by filling the bottom of a saucepan with water and heat it over medium heat until it starts to simmer. Place a heat safe glass or metal bowl on top of the pan. The water should not touch the bowl, or the eggs will start to scramble.
Add the egg yolks and half of the sugar (¼ cup; save the remaining sugar for later) to the bowl and whisk continuously for 8-10 minutes or until the eggs start to turn a pale-yellow color and have become very fluffy. To see if it’s ready, dip a spatula or spoon into the eggs and drag your finger through the middle. The eggs should stay separated on spoon and not run back together.
6 egg yolks, ½ cup granulated sugar
Add the chocolate a little at a time along with the butter and a small splash of the heavy cream (save the bulk of the heavy cream for a later step).
8 ounces dark chocolate, 1 tablespoon unsalted butter
Stir with a spatula as you continue to add the chocolate until it’s smooth and glossy. Then, stir in the salt.
⅛ teaspoon salt
If the chocolate is too thick, pour in another dash of heavy cream to make it smooth. Use pot holders to carefully remove the bowl from the saucepan.
Use an electric mixer with the whisk attachment to whip the remaining heavy cream, remaining ¼ cup of sugar and vanilla together in a large bowl until stiff peaks form.
1 teaspoon pure vanilla extract, 2 cups heavy cream
Fold half of the whipped cream into the chocolate mixture until smooth. Cover and refrigerate the remaining cream in the fridge for later.
Pour the mixture evenly between 4 (8-ounce) ramekins or jars. Chill in the refrigerator for 3-4 hours or until set.
Spoon the remaining whipped cream on top then serve with fresh berries if desired.