In a bowl, beat the buttermilk, egg, butter, vanilla and the sugar until smooth.
Add the flour, baking soda salt and apples, gently mix just until blended.
Spoon into well greased muffin cups.
In another bowl, mix all the topping ingredients and using your fingers mix well to combine. Sprinkle this on each muffin and bake in a preheated 376 oven for 20 min or until a toothpick when inserted in the center of the muffin comes out clean. Let cool for 30 min then serve.