Preheat the oven to 180°C/gas mark 4. Line a 12-hole cupcake tin with 12 cupcakes cases. Put the cocoa powder and 60ml boiling water in a small bowl and whisk. Stir in the sunflower oil and set aside to cool.
In a stand mixer, beat together the butter, sugar and vanilla extract for 5 minutes until light and fluffy. Beat in the eggs one at a time, adding a little flour after each addition to stop the mixture splitting. Beat in the cocoa mixture.
Sift over the remaining flour and baking powder, then gently fold in with a spatula until the mixture is smooth. Evenly distribute the mixture amongst the cake cases, then bake for 25 minutes or until a toothpick inserted into the middle comes out clean.
Turn out on to a wire rack and allow to cool completely. While the cakes cool, start on your icing. Set a medium bowl over a small pan of simmering water, making sure it doesn’t touch the water. Add the chocolate and allow it to slowly melt, stirring occasionally. Take it off the heat and set aside to cool slightly.
In a large mixing bowl, beat the butter and vanilla extract together with an electric hand whisk for 2 minutes until pale and soft. Sift together the icing sugar and cocoa powder. Add 1/3 of the icing sugar mixture and beat on a low speed so the icing sugar doesn’t billow out. Beat on a higher speed until smooth. Add half the remaining icing sugar and repeat, then add the last of the icing sugar and continue to beat for 1-2 minutes until pale and fluffy. Pour in the melted chocolate and beat together for another minute until smooth.
Once the cupcakes are completely cool, use a spoon to carve out a small well in the middle of the cake, being sure not to throw away the removed piece of cake. Fill with 1 tsp of the chocolate hazelnut spread, then replace with the piece of removed cake. Repeat with all the remaining cakes.
Fit a piping bag with a 1cm nozzle. Fill with the chocolate buttercream and pipe on to each cake to resemble the ‘poop’ emoji. Decorate with googly eyes and a ‘smile’ made with small crescents of white paper.