In a large bowl, combine the flour, brown sugar, baking soda and salt. Stir in the buttermilk, butter, vanilla and maple flavoring if desired, until combined. Spread into six greased 13-in. x 9-in. baking pans.
Bake at 350° for 35-40 minutes. Cool on wire racks. Reduce heat to 250°. Break mixture into pieces. Cover and process in batches in a food processor until small pieces are formed; return to baking pans. Bake for 1 hour or until light brown and crisp, stirring every 15 minutes. Store in airtight containers. Serve as a cereal with milk.