• Preheat oven to 350°F (175°C). Grease a 9×9-inch baking pan or similar-sized pan.

Make the crumb topping:

• In a bowl, combine butter, flour, brown sugar, and cinnamon.

  Use a fork or fingers to mix until crumbly.

  Set aside.

Make the cinnamon swirl:

• In another bowl, mix softened butter, cinnamon, flour, and brown sugar until combined.

  Set aside.

Prepare the cake batter:

• In a large bowl, cream the softened butter until smooth.

  Mix in the applesauce and vanilla extract until well combined.

  Beat in the eggs one at a time.
• Stir in the flour and baking powder alternately with the milk.

  Mix just until combined; do not overmix.

Assemble the cake:

• Pour half of the batter into the prepared pan and spread evenly.

  Spoon the cinnamon swirl mixture over the batter.

  Add the remaining batter on top and gently spread.

  Sprinkle the crumb topping evenly over the surface.

Bake for 40–50 minutes, or until a toothpick inserted into the center comes out mostly clean.

• Cool in the pan for at least 15 minutes before slicing and serving.