Line a pie pan, 10 – 12 inch (20 – 24 cm) with aluminum foil only if the tart will be removed from the pan for serving. Don’t line pan if tart will be served directly from pan.
Melt chocolates on top of a double boiler, over simmering water. Remove from heat and let chocolate thicken a little. Combine chocolate with nuts, if desired.
Pour chocolate mixture into pan and cover bottom completely. As chocolate cools and thickens, with a metal spatula, extend chocolate to the sides of pan until all pan is covered and the chocolate crust is complete. Refrigerate until chocolate turns hard.
Place marshmallows with milk and sugar in a medium size saucepan and heat stirring until marshmallows are dissolved. Remove from fire and let it cool. Add liquor or extract. Let it cool.
Whip cream until thick and add, folding carefully, to milk and marshmallow mixture. Add coloring if desired.
Remove crust from refrigerator and peel off aluminum foil. Pour, mint cream carefully into chocolate crust and return to the refrigerator. Garnish with chocolate shavings.
Remove from refrigerator 40 minutes before serving to allow chocolate crust to soften.
Tart can be kept in the freezer.