Heat the oven to 350°F (175°C). Grease a 9 x 5-inch loaf pan and line it with parchment paper, leaving enough overhang on the long sides to lift the finished loaf out easily.

Whisk the flour, baking powder, salt, and poppy seeds together in a medium bowl. In a separate bowl, rub the lemon zest into the granulated sugar before whisking in the eggs, oil or melted butter, milk, lemon juice, and vanilla.

Add the dry ingredients to the wet mixture and stir just until no dry flour remains. Do not overmix, because excessive stirring can make the loaf firm instead of tender.

Pour the batter into the prepared pan and smooth the surface. Bake for 50–60 minutes, until the center springs back lightly and a skewer inserted in the middle comes out clean or with a few moist crumbs.

If the top begins to brown too quickly, loosely tent the pan with foil for the remainder of baking. Cool the loaf in the pan for 10–15 minutes, then transfer it to a wire rack to cool completely.

Whisk the confectioners’ sugar with 2–3 tablespoons of fresh lemon juice, adding the juice gradually until the glaze is thick but pourable. Stir in the optional lemon zest, drizzle over the cooled loaf, and allow the glaze to set before slicing.