In a small bowl, soak poppy seeds in 3/4 cup milk and 11/2 teaspoons vanilla for 1 hour. Meanwhile, separate eggs. Let egg whites, yolks and the butter stand at room temperature for 30 minutes. Grease two 8- or 9-inch round cake pans. Line bottoms with parchment paper; grease again and lightly flour. Set aside. In a medium bowl, combine flour, baking powder and salt; set aside.