You will need:
12 ounces semisweet chocolate, chopped
2 14-ounce cans sweetened condensed milk
1½ cups miniature marshmallows
Heat the milk and pour over the chocolate; stir until melted. Stir in the marshmallows. Pour into a parchment-lined 8-inch square baking pan and refrigerate until firm, at least 12 hours. Cut into 36 squares.