Preheat oven to 350 degrees. Grease and flour an 9x5-inch loaf pan; set aside. In a medium bowl, stir flour, sugar, baking powder, salt, and poppy seeds. Set aside. In a small bowl, whisk together sour cream, eggs, lemon zest, and lemon juice. Pour sour cream mixture into flour mixture, stirring just until combined. Pour batter into prepared loaf pan. Bake 35 to 40 minutes or until golden and thin skewer inserted in center of loaf comes out clean. Meanwhile, in a small saucepan, stir together remaining 1/3 cup sugar, water, and lemon juice. Cook and stir over medium-low heat until sugar dissolves and syrup is clear. Set aside. Cool bread in pan 10 minutes. Loosen edges of loaf with a knife, invert loaf onto cooling rack to remove bread and turn right-side-up on rack. With thin skewer, poke holes in bread; slowly pour syrup over bread and allow it to soak in. I place a plate under the rack just in case. Cool completely. Once bread is cool, whisk together powdered sugar, milk, and lemon juice. Pour over bread, allowing it to run down sides.