Heat the oven to 180°C conventional, 160°C fan, or 350°F. Grease and line a 900 g/2 lb loaf tin measuring approximately 23 x 13 cm with baking parchment.

Beat the softened butter, caster sugar, and lemon zest for 2–3 minutes until pale and fluffy. Add the eggs one at a time, beating well after each addition; if the mixture curdles, mix in a spoonful of the flour.

Fold in the self-raising flour and baking powder just until no dry streaks remain. Toss the blueberries gently with the tablespoon of plain flour, then fold them into the batter at the very end.

Spoon the batter into the prepared loaf tin and level the top. Bake for 45–55 minutes, until golden and a skewer inserted in the center comes out clean or with a few moist crumbs.

If the top begins to brown too quickly, cover the loaf loosely with foil for the remaining baking time. Leave the cake in the tin for 10–15 minutes after baking.

Pierce the warm cake repeatedly with a skewer. Mix the lemon juice and granulated or caster sugar, then spoon or brush the drizzle over the surface so it can soak into the crumb.

Allow the cake to cool completely before removing it from the tin. For an optional finish, mix the icing sugar with enough lemon juice to make a thick but pourable glaze, then drizzle it over the cooled loaf and decorate with blueberries or lemon zest.