Place the milk, brown sugar, and extract in a heavy medium-size saucepan,
and stir to mix. Place the saucepan over medium-high heat, and, stirring constantly,
heat until the mixture begins to reach a boil. Reduce the heat to medium or
medium-low, and add 20 of the marshmallows. Continue to heat, stirring constantly,
until the marshmallows begin to melt.
Remove the saucepan from the heat, and whip the mixture with a wire whisk
until it becomes frothy.
Place 6 of the remaining marshmallows in the bottom of each of 2 mugs. Pour
the butterscotch mixture over the marshmallows, and serve immediately.