Preheat oven to 400 degrees Fahrenheit.
Combine all dry ingredients and stir until well mixed. Add vanilla extract, milk and pureed blackberries to dry mix and knead until all ingredients are mixed.
Form dough into flat logs about 6 inches wide and 1 inch high. Bake on lightly greased cookie sheet for 20 minutes. Remove from oven and allow to cool for 10 minutes then cut logs into 1 inch slices.
Place slices on greased cookie sheet and bake for 15 to 20 minutes until the slices are as dry and crunchy.
Cool and refrigerate.
2 to 3 dozen.