Combine flour, granulated sugar, baking powder, baking soda, cinnamon, and salt in a small bowl.
Whisk egg, milk, and vegetable oil in another bowl.
Add dry ingredients to wet ingredients and stir just until combined, avoiding overmixing.
Mix streusel ingredients — flour, cinnamon, brown sugar, walnuts — in a bowl.
Cut softened butter into streusel mixture until crumbly.
Spray jumbo muffin tin with cooking spray.
Spoon a heaping tablespoon of batter into each muffin cup bottom.
Add a tablespoon of apple butter over each batter portion, then sprinkle with streusel topping.
Distribute remaining batter evenly over each muffin and top with remaining streusel.
Bake at 425°F for 5 minutes, then reduce temperature to 375°F and bake 13-15 more minutes.
Test doneness with a toothpick; muffins are done when it comes out clean.
Mix powdered sugar with apple cider or heavy cream until smooth and drizzle over cooled muffins.
Store muffins in an airtight container at room temperature.