Make the crumb topping: combine sugars, cinnamon, melted butter, & cake flour; stir well. If your crumb topping is still too wet add up to ¼ cup more cake flour. You want it to be a consistency you can easily crumble between your fingers. Set aside.
Preheat oven to 325. Grease an 8x8" baking dish.
Using an electric mixer mix cake flour, sugar, salt, & baking soda together. Add butter & mix. Mixture will become crumbly looking & a little dry. Add egg, egg yolk, yogurt/buttermilk, & vanilla. Beat until light & fluffy.
Pour mixture into greased baking pan using a rubber spatula to smooth it out.
Add crumb topping by using your fingers to break apart the crumbs & sprinkle them over the batter. (Don't press them into the batter)
Bake for 35-40, until toothpick inserted in center comes out clean.
Let cool for 30 minutes & dust with powdered sugar before serving, if desired.
Recipe by THE SEMISWEET SISTERS at https://www.thesemisweetsisters.com/2014/07/23/new-york-style-crumb-cake-recipe/