In a large saucepan melt the marshmallows, chocolate pieces and water over low heat, stirring constantly. Remove from heat to cool slightly.
Add remaining ingredients except the oats and pecans to stand mixer bowl. Pour melted chocolate and marshmallow mixture, turn on low and blend. If you don't have a mixer, doing this by hand is a workout, but the payoff is an amazing cookie!
Next, slowly add the oats and pecans and mix to combine. Refrigerate for 20-30 minutes to firm dough.
Preheat the oven to 350˚F.
Drop by rounded tablespoon onto cookie sheet. Bake for 12 minutes.
Mom's original recipe used 1/2 cup Crisco, but I substituted with butter.