Preheat the oven to 375°F. 

Lightly spray with cooking spray or butter a standard 12-cup muffin tin, or line the tin with muffin tin liners. If using standard muffin liners, grease the top of the pan around each muffin as the muffins will crown over the edges a bit.

In a bowl (or I use a 4 cup measuring cup), using a fork or whisk, stir together the flour, baking powder, baking soda, cinnamon, ground coriander, and salt. 

In a medium-sized bowl, beat together the butter and sugar until well combined and fluffy. 

Add the eggs one at a time, beating well after each addition.

Beat in the vanilla and orange peel. 

Using a spatula, add in ½ the flour mixture. Gently stir together, being careful not to over mix. Just stir until almost combined.

Stir in the buttermilk, blending until again, just barely combined.

Add the remaining flour mixture. Fold and stir just until combined. There can be small clumps. They will blend a bit more as you add in the blackberries. 

Add the blackberries to the batter, stirring just to combine and to evenly distribute. 

Scoop the batter by the heaping 1/4-cupfuls into the prepared muffin pan; a muffin or ice-cream scoop works well here.

Sprinkle about 1 teaspoon coarse sugar atop each muffin, if desired    

Bake the muffins for about 30 minutes, until they're light golden brown on top, and a toothpick inserted into the middle of one of the center muffins comes out clean. 

Remove the muffins from the oven, loosen their edges from the pan, and after about 5 minutes transfer them to a rack to cool.

serve these puppies warm with butter!