1) Preheat the oven to 150C/Gas 2.
2) Line the bun tin/fairycake tin with paper liners and spray the liners with vegetable spray.
3) Shave 140g of chocolate and put it into a bowl. Cut the remaining 85g of chocolate into roughly 1.5cm pieces, set aside.
4) 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.
5) 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).
6) Scoop about 60g of the batter into each mould, 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.
7) Immediately, while hot, add a chunk of the remaining chocolate in the center of each, by gently pushing it through the top of the cake in the center. Cool the tin on a rack for 10 minutes and then unmold them.
8) Dust with powdered sugar and serve warm.