Step 1

Preheat oven to 375°F. Line a standard 12-cup muffin pan with paper liners; set aside.

Step 2

In a large bowl, whisk together flour, sugar, oats (if using), baking powder, cinnamon, salt, and nutmeg.

Step 3

In a medium bowl, whisk together buttermilk (or milk), melted butter, oil, eggs, and vanilla extract.

Step 4

Add the wet ingredients to the dry ingredients. Stir just until combined, being careful not to over-mix. The batter may be lumpy, which is fine.

Step 5

Fold in the blackberries.

Step 6

Divide batter evenly among the prepared muffin cups, filling each cup almost to the top. Sprinkle coarse sugar on top, if desired.

Step 7

Bake for 17-20 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs attached.

Step 8

Transfer muffins to a wire rack to cool. Serve warm or at room temperature.