Position the oven rack to rack position 3 in Wolf oven. Preheat oven in BAKE at 325°F. Grease Bundt pan with butter. Sift together flour, sugar, poppy seeds, salt, baking soda and baking powder in large mixer bowl. Whisk together butter, buttermilk, eggs, lemon zest and vanilla in small bowl. Beat egg mixture into dry ingredients until smooth. Pour batter into prepared pan and place in center of oven. Bake 55 to 60 minutes or until knife inserted into center of cake comes out clean. Remove cake from oven and allow to cool for 30 minutes before turning out onto cooling rack. Meanwhile, combine powdered sugar and lemon juice with a whisk. Pour oven warm inverted cake. Allow to cool before serving.