Cobbler, Rhubarb

Ingredients

• 1 pound fresh rhubarb stalks, cut into 1/2" pieces (3 cups), or 3 cups frozen rhubarb, thawed after measuring
• 1 cup light brown sugar, packed
• 2 cups cake flour (not self-rising), sifted
• 3/4 teaspoon baking powder
• 1/2 cup plus 2 tablespoons granulated sugar
• 1 stick cold unsalted butter, cut into 1/2" cubes
• 1/3 cup whole milk
• 2 large eggs,1 separated