1. Preheat the oven to 350 degrees Fahrenheit. Grease 14 eight-ounce jars.
2. In a separate bowl, use a handheld mixer to beat the egg whites until stiﬀ peaks form. Set aside.
3. In a stand mixer, beat together the granulated sugar and egg yolks until thick and creamy. Mix one-fourth cup of the melted chocolate and butter into the egg yolks. Continuing to mix, slowly pour the remaining melted chocolate mixture into the egg yolks until all is incorporated. Fold the egg whites into the chocolate mixture.
4. Spoon four to five tablespoons of the cake batter into each greased jar. Place the jars two inches apart on a large baking sheet. Bake for 25 to 30 minutes, until the tops of the cakes start to crack.
5. Remove from the oven and let the jars cool. Dust with confectioners’ sugar before serving. Serve warm or at room temperature.
6. In a double boiler over simmering water, melt the chocolate and butter until smooth. Remove from the heat and allow to cool slightly.