Preheat oven to 375°F (190°C). Grease or line a jumbo muffin pan.
Cream sugar, butter, vanilla, and salt until fluffy. Beat in eggs one at a time.
Mix flour, baking powder, and cinnamon in another bowl.
Gradually add to creamed mixture, alternating with milk.
Fold in apples and walnuts.
For the topping, combine sugar, flour, butter cubes, and cinnamon until crumbly.
Fill muffin cups ¾ full with batter, sprinkle topping over each.
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