Preheat the oven to 350 degrees F and line a cupcake pan with 4 paper liners.

In a mixing bowl, beat the butter and 1/4 cup sugar until light. Add the egg, lemon zest, and half the lemon juice, then mix in the flour and baking powder. Stir in the milk until the batter is smooth.

Divide the batter evenly among the liners and bake for 15 to 18 minutes until a toothpick comes out clean. Let the cupcakes cool completely.

In a clean bowl, beat the egg whites with cream of tartar until soft peaks form. Gradually add the remaining 1/4 cup sugar and continue beating until stiff, glossy peaks hold.

Spoon the meringue into a piping bag and pipe ghost shapes onto each cooled cupcake. Return the cupcakes to the oven for 4 to 5 minutes until the meringue is lightly set.