the taste of fall - part 3 : Apple Streusel Muffins

I try to make something special for breakfast on Saturday mornings. These muffins are really easy and they taste like they came from a bakery.
Apple Streusel Muffins

2 cups flour
1 teaspoon baking powder
1/2 teaspoon baking soda
1/2 teaspoon salt
1/2 cup butter, softened 
1 cup white sugar
2 eggs
1 1/2 teaspoons vanilla
2 Granny Smith apples, peeled and diced small

Topping:

2/3 cup [...]