Prepare Pan

1. Coat pan with nonstick cooking spray
2. Lay one piece of parchment across length of pan, over hanging the sides. Coat with nonstick spray
3. Repeat with remaining piece of parchment, laying it across width. Coat with nonstick spray and all-purpose flour, shaking out excess

Make Batter

1. In a medium bowl, combine dry ingredients. Whisk to thoroughly combine and set aside
2. In the bowl of a standing mixer fitted with the paddle attachment, beat butter and sugar on high until light and fluffy, about 3 minutes. Add eggs, one at a time, beating to combine after each addition. Beat in orange zest and vanilla. Scrape down bowl
3. With mixer on low speed, alternate adding in dry ingredients and sour cream. Begin with ⅓  of the dry ingredients, beat to combine, add ½ of the sour cream, beat to combine.
4. Repeat steps, finishing with dry ingredients. Scrape down bowl. Beat batter for 15 seconds. Set batter aside

Make Crumb Topping, Layer & Bake

1. In the bowl of a food processor, combine dry ingredients. Pulse to thoroughly combine
2. Add butter and pulse until mixture resembles coarse meal, about 30, 1-second pulses
3. Spread ½ of cake batter evenly into prepared pan. Top with ½ of the crumb mixture
4. Spread remaining cake batter, then top with remaining crumb mixture
5. Bake for 50-60 minutes, rotating halfway through bake time. Cake is done when a skewer inserted into the center come out clean. Remove from oven to a cooling rack. Cool for 30 minutes

To Serve

1. Remove cake from pan to a cutting board by grasping long sides of the parchment sling
2. Slice and dust with powdered sugar (optional). Store in a tightly sealed container for up to 5 days