Preheat the oven to 200°C, fan 180°C, gas 6. Line a 6-hole muffin tin with paper cases. Make the muffins according to packet instructions (you'll need the egg and milk for this), then let them cool for 10 minutes on a wire rack.
When cool, cut the rounded top off each muffin to make a flat surface. Turn upside down on a board and gently peel off the cases.
Roll out the icing to a thickness of about 5mm. Cut out 6 x 13cm (approx) diameter circles, re-rolling the trimmings, if necessary.
Brush the muffins with the jam then place an icing circle over the top of each one. Press to flatten the top, then make draping folds around the edges to look like floaty ghosts.
Get the kids to help draw on eyes with the writing icing. Leave to set for 10 minutes then serve.