Preheat oven to 325°. Line a 9×9″ baking pan with parchment paper, leaving overhang on 2 sides. Whisk flour, baking powder, baking soda, and salt in a medium bowl. Whisk eggs, egg yolk, yogurt, milk, granulated sugar, brown sugar, vanilla extract, ¾ cup reserved ghee, and 1 tsp. reserved caramelized milk solids in a large bowl to combine. Sift in dry ingredients and fold just until no dry spots of flour remain (batter will be thick and slightly lumpy). Spoon half of batter into prepared pan; spread to edges. Sprinkle half of streusel evenly over, then dollop remaining batter on top and gently spread into an even layer. Sprinkle remaining streusel on top and gently pat to adhere to batter.