Preheat the oven to 300 degrees F.
Line the cupcake pan with paper liners and spray the liners with vegetable spray.
Shave 5 ounces of chocolate and put it into a bowl. Cut the remaining 3 ounces of chocolate into roughly 1/2-inch pieces, set aside.
Combine the butter and cream in a small saucepan over medium-high heat. When the cream mixture comes to a simmer, pour it over the shaved chocolate and stir gently to melt the chocolate.
In a medium bowl, whisk together the eggs, sugar, mayonnaise, cornstarch, cinnamon, and salt just until the sugar has dissolved. Pour the chocolate mixture into the egg mixture and gently mix just until combined. (Mixing too much will prevent the eggs from rising in the oven.) Scoop about 1/4 cup of the batter into each mold, it should come about 3/4 of the way up the sides. Bake until a toothpick inserted in the center comes out clean, 40 to 45 minutes. Do not over bake. Immediately while hot, add a chunk of the remaining chocolate in the center of each, by gently pushing it through the top of the cupcake in the center. Cool the pan on a rack for 10 minutes and then unmold them. Dust with powdered sugar and serve warm.
Be certain to add the chocolate chunks while the cakes are still quite hot from the oven otherwise the crust will form and you will damage the appearance. The mayonnaise is here to add moisture to the cake. You could omit it with out adjusting the recipe but it is has an amazing effect. Serve this as a plated dessert by removing them from the paper and adding warm bananas.