1. Heat oven to 350 degrees F.
2. Grease a 15 x 10 x 1-inch baking pan. Lightly dust the pan with all-purpose flour; gently shake out any excess flour.Cake:
3. Combine cake mix, sour cream, oil, eggs, cinnamon and nutmeg in large bowl. Beat according to package directions. Pour batter into prepared pan.
4. Bake in 350 degrees F oven 20 minutes or until wooden pick inserted in center comes clean.Crumb Topping:
5. Stir together flour, brown sugar, cinnamon, nutmeg and melted butter in medium-size bowl until mixture is evenly moistened and comes together in clumps.
6. Remove cake from oven. Sprinkle crumbs over top (this will be a thick covering). Return to oven and bake 15 minutes or until crumbs are slightly set. Remove pan to wire rack and let cool completely.Sour Cream Glaze:
7. Whisk together the 1/2 cup powdered sugar and sour cream in a small bowl until well blended. Dust the top of the cake evenly with the remaining 2 tablespoons of powdered sugar. Then drizzle evenly with the Sour Cream Glaze. Store the cake, tightly covered, at room temperature for up to 3 days.