Preheat oven to 350°F and grease a 9" springform pan.
In a mixing bowl, whisk together the applesauce, sour cream, egg, and vanilla until smooth.
1 cup unsweetened applesauce, 1 cup sour cream, 1 large egg, 1 teaspoon vanilla extract
Then, stir in both the granulated sugar and light brown sugar until everything is nicely combined.
½ cup granulated sugar, ½ cup light brown sugar, packed
Using a separate bowl, stir together the flour, salt, cinnamon, nutmeg, and baking soda.
2 cups all purpose flour, ½ teaspoon salt, 1 teaspoon cinnamon, ½ teaspoon nutmeg, 1 ½ teaspoons baking soda
Gradually add the dry ingredients to the wet ingredients, stirring just til combined.
Pour the batter into your prepared pan and smooth the top with a spatula.
For the crumb topping, mix together the oats, flour, sugar, cinnamon, and melted butter in a bowl until it's crumbly.
¾ cup old fashioned oats, 2 Tablespoons all purpose flour, ½ cup light brown sugar, packed, ½ teaspoon cinnamon, 4 Tablespoons butter, melted
Sprinkle the crumb topping evenly all over the top of the cake batter.
Bake for 30 to 40 minutes, or until a toothpick comes out mostly clean and the cake is lightly golden.
While the cake is cooling, let's make the glaze - whisk together the powdered sugar and milk - and a little lemon zest if you're feeling fancy.
1 cup powdered sugar, 2 Tablespoons milk
Once the cake has cooled, drizzle the glaze over the top, slice yourself a nice big piece, and enjoy!