Preheat the oven to 350°F
In a mixer or food processor or bowl... combine the flour, baking powder, and sugar. Slowly add the butter 1 Tablespoon at a time. Pulse/mix/cut the butter into the dry ingredients. You want it to look like wet sand... and clump when you pinch it.
Divide this streusel mixture into ⅔ and ⅓. Press the ⅔ into the bottom and approximately 1 to 1½ inches up the side of a springform pan. You don't want it TOO thick in the corners, so press it in. Thickness should be about ¼ - ⅓ inch across bottom and sides.
Bake this for 15 minutes
While the shell is baking, combine the Applesauce, Cornstarch, Vanilla Extract, and Cinnamon in a medium bowl. Make sure not to leave any lumps of cinnamon or cornstarch.
Add the applesauce mixture to the pre-baked shell.
Crumble the rest of the streusel mixture over the applesauce evenly. Use your fist to squeeze it so you get bigger bits as well as just crumbs.
Bake 35 minutes.
Remove from oven and let cool on a rack.