Preheat the oven to 350 degrees. Grease or line a muffin tin and set aside.
Combine the flour, cocoa powder, baking soda, baking powder and salt in a medium bowl foryou Harry Potter Inspired Cauldron Cakes.
In a separate bowl, mix together the oil and sugar until thoroughly combined.
Add the egg and vanilla to the oil mixture and beat until fully incorporated.
Add in 1/3 of the flour mixture and mix well. Add half of the milk and mix again.
Add another 1/3 of the flour and mix well. Add the second half of the milk and combine thoroughly.
Finally, add the last of the flour mixture and mix until completely incorporated.
Spoon the batter into the muffin tins, filling them about halfway. Bake for 12–15 minutes, or until a toothpick inserted in the center comes out clean.
Remove the cupcakes from the oven, then, with a knife, remove each cupcake from the tin to a cooling rack. Let cool completely, 45–60 minutes.
While the Harry Potter Inspired Cauldron Cakes cool, combine all the ingredients for the filling in a small saucepan over medium heat. Stir well until the mixture thickens, about 7 minutes, then remove it from the heat and cool completely.
Using an electric handheld mixer, mix the filling again for 5 minutes or until it becomes fluffy and light.
Once the filling is fluffed, use your thumb or a small spoon to press a hole in the cupcakes, creating a “cup” inside each one.
Fill each cup with the filling and let stand while you make the icing.
To make the icing, beat the butter on medium speed with an electric handheld mixer until it is soft and creamy. While beating, gradually add in the powdered sugar, stopping the mixer every now and then to scrape down the sides with a spatula.
Once the sugar and butter are thoroughly incorporated, add the vanilla and beat again.
Add the heavy cream or milk, 1 tablespoon at a time, until the desired consistency is reached.
Let stand for 5 minutes, then frost your Harry Potter Inspired Cauldron Cakes and serve.