eggs 1 cup sour cream quarter cup ( half stick) butter, melted 1 cup diced unpeeled apple, preferably a tart apple such as Granny Smith or Greenings Heat oven to 190ºC . Grease muffin cups or use foil baking cups. Put streusel topping ingredients into a medium-size bowl. Mix with a fork, then crumble with fingers until mixture looks like chopped walnuts. To make the muffin batter, thoroughly mix fllour, sugar, baking powder, cinnamon, allspice, baking soda, and salt in a large bowl. Break eggs into another bowl. Add sour cream and melted butter, and whisk until well blended. Stir in diced apple. Pour egg mixture over flour mixture and fold in just until dry ingredients are moistened. Scoop batter into muffin cups. Top each muffin with about 2 teaspoons of the streusel topping. Bake 20 to 25 minutes, or until browned. A toothpick inserted into the center should come out clean. Remove from pans and let cool at least 1 hour before serving.