Preheat the oven to 350°F
. Mix the whole wheat flour, brown sugar, and salt in a very large bowl or container until the ingredients are thoroughly combined.
In a large mixing bowl, combine the buttermilk and baking soda until smooth.
Add the buttermilk mixture to the flour mixture, and stir until the flour mixture is evenly coated.
Add the maple flavoring, vanilla, and butter, and stir to evenly incorporate.
Spread the mixture evenly on baking sheets.
Bake until nicely browned (about two hours).
Let cool completely, then crumble into fine pieces and toast in a warm (250°F) oven.