Whisk the flour, baking soda, baking powder, and salt in a large bowl.
To make the crumb topping, whisk both kinds of sugars, salt, and cocoa powder in a mixing bowl. Stir in the melted butter. Add the flour and stir with a fork until the mixture forms clumps. Set the topping aside while you make the cake.
Beat the butter and sugar until the mixture is light and fluffy. Beat in the egg and extra egg yolk and then add the yogurt, milk, and vanilla. Add the dry ingredients in three batches mixing between each until just combined.
Spread the batter in a prepared 8″ springform pan and sprinkle the crumb topping over the top of the vanilla batter and bake.