Preheat oven to 350°F (180°C).
Mix together topping ingredients and set aside. Combine the first seven ingredients for the batter, stir well and set aside. In another bowl, beat together egg, oil, vanilla and yogurt. Pour liquids into dry ingredients and stir just until dry ingredients are moistened. Spoon batter into prepared muffin tins. Sprinkle topping over muffins and press firmly into batter.
Bake 20 – 25 minutes.