We think your neighbors will certainly agree: These extra-chocolaty fudge hearts are best when shared. But don't forget to save a few for yourself.
Butter an 8-inch square baking pan. In a heavy 2-quart saucepan, combine the butter, milk, sugar and salt and stir over low heat until the butter has melted. Bring the mixture to a boil over medium-high heat. Boil for 5 minutes, stirring constantly. (Only older kids and parents should be in charge of this step, since the mixture will be quite hot and bubbly.) Remove from the heat and stir in the miniature marshmallows until they have fully melted. Stir in the vanilla extract. Then slowly pour in the chocolate chips, stirring as you go, until the mixture is smooth.
Turn the mixture into the buttered pan and smooth out with a plastic spatula, if necessary. While the fudge is still warm, score it into 16 squares. Once the fudge has cooled fully (which can take at least an hour), cut it into squares with a sharp knife. For heart-shaped pieces, gently press a mini heart-shaped cookie cutter onto each square and remove excess. Makes 16 2-inch squares (or slightly smaller hearts).