Preheat oven to 350 F.
In a double boiler, melt chocolate and butter, reserve.
In a large mixing bowl, whisk together eggs, sugar, cornstarch, vanilla and salt. Slowly stir the chocolate into the egg mixture until thoroughly combined. Cover the bowl and refrigerate for at least 2 hours or overnight.
Scoop mixture evenly into 6 cups in a mini-cheesecake pan, or six ounce oven-proof baking cups. Bake in preheated oven for 15 minutes. Turn and bake for 10 minutes more. They will be done when the outside has risen slightly above the sides of the pan and the center is still soft. Let cool completely.
Unmold the cakes by pushing the bottom disc of the pan upward; remove the disc from the bottom of each cake. Place each cake on a plate and serve.
Recipe adapted from Chicago Metallic