I would like to make the grasshopper pie but have some family members who are allergic to alcohol. What could I substitute for the creme de menthe and creme de cacao blanc?
For a non-alcoholic version of Grasshopper Pie simply replace the creme de cacao and creme de menthe with 1/2 teaspoon (ie 2.5 mls)of peppermint extract (and note that you don't need to make up the lost liquid volume with anything else). The flavour is not quite as rounded as the alcoholic version but it is suitably minty and complements with the chocolate crust.
However, do try to use a good-quality natural peppermint extract rather than an artificial one. Also as you don't get any green colouring from the creme de menthe you will need to add at least a little green food colouring to the marshmallow mixture, otherwise it will be white.