Step 1Heat oven to 350 degrees. Butter and flour an 8-inch loaf pan.
Step 2In a bowl, combine lemon zest and sugar and rub with your fingers until it looks like wet sand. Whisk in buttermilk, 3 tablespoons lemon juice and eggs. In a separate bowl, whisk together flour, baking powder, baking soda and salt. Whisk dry ingredients into the batter, then whisk in oil and poppy seeds.
Step 3Pour batter into prepared pan. Bake until a toothpick inserted in the center emerges clean, about 1 hour. Let cool in pan until warm to the touch, then turn out onto a baking rack set over a rimmed baking sheet. Turn cake right side up.
Step 4Whisk together remaining 4 teaspoons lemon juice and the confectioners’ sugar. Use a pastry brush to spread glaze evenly over top and sides of cake. Cool completely before slicing.
