1. Position rack in center of oven and preheat to 350 degrees F. Butter 12 standard-size (1/3-cup volume) muffin cups or line cups with muffin papers.
2. Whisk first 4 ingredients in a large bowl to blend well.
3. Whisk buttermilk, eggs, sour cream and oil in a medium bowl to blend; whisk in herbs and lemon peel.
4. Stir buttermilk mixture into flour mixture. Divide batter among prepared cups. Brush tops lightly with melted butter.
5. Bake muffins 20 minutes. Brush tops with butter. Continue baking until golden on top and tester inserted into center comes out clean, about 15 minutes longer. Turn muffins out onto rack. Serve warm or at room temperature.