In a medium bowl, combine 1/4 cup flour, 2/3 cup sugar, and 1 teaspoon cinnamon. Cut in butter until mixture resembles coarse crumbs. Set aside.Cake
In a large bowl, combine 2 cups flour, 3/4 cup sugar, baking powder, and salt. Cut in butter until mixture resembles coarse crumbs.
Crack an egg into a measuring cup and then fill add milk to make 1 cup. Stir in vanilla. Pour into crumb mixture and mix just until moistened.
Spread cake batter into a parchment lined 5 quart or larger crockpot. Sprinkle top with streusel.
Cover and cook on high for 2 - 2 1/2 hours or until a toothpick inserted into the center of the cake comes out clean. Carefully remove the cake using the parchment paper and let it cool on a baking rack. Serve.