Place an oven rack in the center of the oven and preheat to 160C/Gas 3.
Combine the plain chocolate and water in a small saucepan over medium-low heat. Stir constantly until the chocolate is melted, about 2 minutes. cool for 2 minutes. Whisk in the mascarpone cheese until the mixture is smooth.
Beat the sugar, oil, eggs, and vanilla in a large bowl for 30 seconds. Stir in the mascarpone mixture. Whisk the plain flour, bicarbonate of soda, salt, baking powder, and chocolate chips in a medium bowl. add the dry ingredients to the chocolate mixture. stir until just blended.
Divide the batter among the prepared muffin pans. Bake for 20 to 25 minutes or until a tester inserted into the center of a cupcake comes out with no crumbs attached. Cool the cupcakes completely before dipping, about 1 hour.
For the ganache:
Place the chocolate chips in a small bowl. Combine the double cream and vanilla essence in a small saucepan over medium-low heat. Cook until small bubbles appear on the outside edge of the cream. Pour the hot cream mixture over the chocolate chips. Using a fork, gently stir until all the chocolate is melted and the mixture is smooth.
Dip the tops of each cupcake in the ganache and transfer to a baking sheet. Place the dipped cupcakes in the refrigerator to set, about 15 to 20 minutes. Allow cupcakes to return to room temperature before serving.
Cook's note: For puffier cupcakes allow the batter to rest in the muffin pans for 20 minutes before baking.