Layers of Happiness

1 Preheat the oven to 350F degrees. Generously spray a 9x9 baking pan with nonstick spray. Set aside.
2 Make the crumb topping first: In a small bowl, toss the flour, brown sugar, salt, and cinnamon together.Cut in the cold butter using a pastry blender, a fork, or your hands. Mix to create clumps and crumbs. Set aside.
3 Make the cake: Sift together the flour, baking soda, cinnamon, nutmeg, and salt. Sift two more times and set aside. In a medium bowl, whisk the oil, granulated sugar, brown sugar, egg, egg white, and vanilla together until combined. Pour the wet ingredients into the dry ingredients and stir until almost combined. Try not to overmix the batter. It will be very thick. Fold in apples and walnuts and mix until evenly combined.
4 Spoon/pour the batter into the prepared baking pan. Spread to make an even surface. Pour the crumb topping evenly on top and gently press them down into the batter.
5 Bake the cake for 30-35 minutes, or until the cake appears to be crispy around the edges and the batter doesn't jiggle when the pan is shaken. If the cake still looks uncooked after 30 minutes, bake the cake for 5 more minutes.
6 Make the glaze: In a small bowl, whisk the melted butter, brown sugar, granulated sugar, milk, vanilla, and salt together. Add the powdered sugar and whisk until just combined. Drizzle over cake. Enjoy cake warm or at room temperature. Cover cake tightly and store at room temperature or in the refrigerator for up to 3 days.