Preheat oven to 375°. Line muffin pan with paper liners.
Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour and next 6 ingredients (through salt) in a large bowl and whisk together. Stir in oats, chopped dates, raisins, and cranberries.
Bring the water to a boil.
In a separate bowl, whisk buttermilk, oil, vanilla, and egg; add to flour mixture, stirring just until moistened. Add boiling water. Stir, and let batter sit for 15 minutes.
Spoon batter into muffin cups. Bake for 20 minutes or until muffins spring back when touched lightly in center. Remove muffins from pans immediately; place on a wire rack to cool.