Topping:

Mix both sugars, cinnamon, and salt in medium bowl. Add warm melted butter and stir to blend. Add flour and toss with fork until moist clumps form (topping mixture will look slightly wet). Set aside.

Cake:

Position rack in center of oven and preheat to 350°F. Butter 13x9x2-inch glass baking dish.

Add flour, baking soda, baking powder and salt into medium bowl and whisk to blend.

Using electric mixer, beat room-temperature butter in large bowl until smooth. Add sugar and beat until light and fluffy, stopping now and then to scrape down sides of bowl.

Add eggs 1 at a time, beating until well blended after each addition. Add 1/3rd of the sour cream and vanilla extract and beat just until blended. Add 1/3 of the flour mixture and beat until just incorporated, stop and scrape bowl down.

Continue to add in additions, sour cream, then flour (twice more of each, for a total of three additions each) until mixture is blended, beating each time just until incorporated and scraping bowl down after each addition is finished blending.

Transfer cake batter to prepared baking dish; this will be very thick. Spread batter evenly with rubber spatula or offset spatula; you may need to use clean hands.

Squeeze small handfuls of topping together to form small clumps. Drop topping clumps evenly over cake batter, covering completely (topping will be thick).

Bake cake until tester inserted into center comes with only a little crumb attached (it’s easiest to test in an area with fewer crumbs, towards the center) and topping is golden brown and slightly crisp, about 40 to 45 minutes. Cool cake in dish on rack at least 30 minutes.

May be made 1 or 2 days ahead. Cool completely. Cover and let stand at room temperature.

Cut cake into squares and serve slightly warm or at room temperature.