I'm sure there are many many versions of this recipe out there, but this is the tried and true one that I use. Mudpies can be a bit touchy. Boil too long and they're a little dry. Boil too short and they're a little soupy. The use of a timer is very important.
1/2 cup butter or margerine
1/2 cup milk
2 cups granulated sugar
1/2 cup cocoa
2 1/2 cups rolled oats (not the big fat ones, although in a pinch, they will work)
Put butter, milk, sugar and cocoa in a saucepan. Bring to a boil stirring often (especially if you have a gas stove). When mixture comes to a boil, let boil for 5 minutes (set timer) stirring constantly. Remove from heat. Stir in rolled oats. Drop by teaspoonfuls onto waxed paper. Let cool.
Makes about 4 dozen.