Preheat oven to 325 degrees. Butter and flour bundt pan. Mix lemon zest with sugar in small bowl. In a large bowl, beat together the butter and sugar with an electric mixer until light and fluffy. Beat in vanilla and eggs one at a time. Beat in lemon juice, baking powder and soda and salt. Mix in the flour until well combined. Stir in poppyseeds. Pour the batter into prepared bundt pan. Bake at 325 degrees for 45 minutes or until a knife comes out clean. Cool cake for fifteen minutes and then flip out of pan. To make icing, combine confectioner's sugar and lemon juice In small bowl and stir until smooth. When cake has cooled, drizzle icing over cake and serve.