Preheat oven to 425 degrees F. Have ready a baking sheet lined with parchment paper.
Stir together buttermilk and cereal. Let stand for about 5 minutes or until cereal is softened and absorbs most of the milk.
In large bowl, combine flour, sugar, baking powder, baking soda and salt. Add butter to mixture and work it into the flour until crumbly. You can do this with your fingers, a food processor or a pastry cutter if you prefer. Once you have a crumbly mixture, add the sugar and stir until evenly mixed. Also, add coconut if using.
Stir milk/cereal into dry ingredients until mixture comes together. It should be fairly dry. Empty onto a workspace and gently knead so that all the flour is worked in. If dough is sticky, add a little more flour (it should not be sticky). Shape dough into a rectangle and sprinkle with add-ins. Fold dough over on itself in thirds, working in the add-ins. Repeat, fold. Shape into circle somewhere around 7 inches.
With a large knife, cut into 8 neat triangles. Arrange a couple of inches apart on the parchment lined baking sheet, and brush tops with whole milk or a little heavy cream. Sprinkle with coarse or sparkling sugar.
Bake for 10 minutes at 425, then reduce heat to 375 and bake for another 10 minutes.