Preheat the oven to 180 degrees Celsius/ 360 degrees Fahrenheit. Line a 12 muffin tin with paper cases.

Place the flour, baking soda, baking powder and unsweetened cocoa powder in a bowl. Chop the semisweet chocolate into small pieces about the size of chocolate chips or use semisweet chocolate chips. Add them to the flour mixture and stir to mix. Set aside.

In another bowl whisk together the egg and the sugar. Add the oil, vanilla extract, and buttermilk. Whisk very well.

Add the dry ingredients to the wet ones and whisk carefully until the dry ingredients are moist. Do not over mix, it is OK if there are still some small lumps in the batter.

Place the batter to the muffin tin. Bake for 20 minutes. Leave to rest in the tin for about 5 minutes, then transfer to a wire rack to cool completely.

Make sure the butter has room temperature before you start. Place the butter in a bowl and mix until light and fluffy, at least 2 minutes.

Slowly and gradually add the icing sugar. Add the vanilla extract or aroma and continue beating until the buttercream is nice and fluffy. Transfer the buttercream to a piping bag fitted with a large star nozzle.

When the cupcakes are completely cool, pipe the buttercream on top.

Twist the Oreo cookies to open them up and place two halves that still have enough of their own white frosting attached to them on the buttercream frosting to form the eyes.

Snap another cookie half in two to form the “eyebrows” of the owls and stick them into the buttercream as well. You can use some of the halves that don't have that much of their own frosting left on for this step.

Use M&M's or large Smarties to form the eyes. If the eyes don't stick to the Oreo frosting very well, smear them with a tiny amount of buttercream (rests from the mixing bowl) on the underside and then stick them onto the cookies.

Form the beak of the owl with another M&M or Smarties.