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

Whisk the flour, baking powder, and fine salt together in a medium bowl. Set the dry mixture aside while you prepare the butter and sugar.

Rub the finely grated lemon zest into the granulated sugar with your fingertips until the sugar feels fragrant and slightly damp. Beat the lemon-scented sugar with the softened butter for 2–3 minutes, until pale and fluffy.

Beat in the eggs one at a time, allowing each egg to blend in before adding the next. Mix in the lemon juice and vanilla extract until the batter is evenly combined.

Add the dry ingredients in two or three additions, alternating with the sour cream. Mix only until no obvious streaks of flour remain, because overmixing can make the loaf firm.

Spread the batter evenly into the prepared loaf pan and smooth the surface. Make sure the batter reaches the corners so the loaf bakes with an even shape.

Bake for 45–55 minutes, until the top is lightly golden and a toothpick inserted in the center comes out with a few moist crumbs. If the top browns too quickly, cover the loaf loosely with foil for the remainder of baking.

Cool the loaf in the pan for 10–15 minutes, then transfer it to a wire rack. Let it cool completely before adding the glaze.

Whisk the powdered sugar with 2–3 tablespoons of fresh lemon juice until the glaze is thick but pourable. Add milk or cream a little at a time only if the glaze needs thinning.

Pour the glaze over the completely cooled loaf and let it set before slicing. For especially neat slices, chill the glazed loaf briefly and cut it with a serrated knife.