Heat the oven to 175 C / 350 F. Line a 9x5 inch (23x13 cm) loaf pan with parchment paper, leaving an overhang on both long sides.

Whisk the flour, baking powder, and salt together in a large bowl. Set aside.

In a separate bowl, rub the lemon zest into the granulated sugar with your fingertips for about 30 seconds until the sugar looks pale yellow and smells fragrant.

Whisk the eggs into the lemon sugar until the mixture is pale and slightly thickened, about 1 minute.

Add the sour cream, elderflower cordial, lemon juice, and melted butter. Whisk until smooth and combined.

Pour the wet mixture into the flour bowl and fold with a spatula until just combined, about 15 strokes. Stop when no dry streaks remain - a few lumps are fine.

Pour the batter into the prepared pan and smooth the top. Tap the pan gently on the counter once to release any large air pockets.

Bake for 50 to 55 minutes, until the top is deep golden and a toothpick inserted into the center comes out with moist crumbs.

Cool in the pan for 10 minutes, then use the parchment overhang to lift the loaf onto a wire rack. Leave it warm, not fully cooled, before glazing.

Whisk the sifted powdered sugar, elderflower cordial, and lemon juice together until smooth and pourable. It should fall slowly off the whisk in a thick ribbon.

Pour the glaze evenly over the warm loaf, letting it drip down the sides naturally. Let it set for 20 minutes before slicing.