In a heavy-bottomed saucepan over medium-low heat, combine the condensed milk and 1 tablespoon of butter. Slowly bring the mixture to a boil, stirring continuously. Continue stirring over the heat until mixture becomes thick and amber in color, about 15 minutes.
While that is simmering, combine crust ingredients in a food processor. That is the flour, butter, and powdered sugar. Mix until resembles wet sand. Pat into an 8-inch square baking dish that has been sprayed with non-stick spray. Bake crust at 375 degrees for 12 to 15 minutes. It will not brown.
Immediately layer marshmallows over crust, return to oven and broil until lightly brown. Allow the marshmallows to cool slightly and set.
Pour the caramel (the sweetened condensed milk that has been cooked down.) over marshmallows and spread evenly using an offset spatula.
Press peanuts into caramel.
Top layer, chocolate
Melt the chocolate at 30-second intervals in the microwave. Stop and stir at each interval. (My microwave took 90 seconds total.)
Pour melted chocolate over peanuts and smooth flat. Allow chocolate to set before cutting. (It hardens in about 15-minutes in the freezer.