Heat oven to 180°C and line a 1kg loaf tin with baking parchment.
Combine the flour, baking powder, bicarbonate of soda, caster sugar, lavender, and lemon zest in a bowl.
Beat the eggs with the yoghurt and melted butter in a jug.
Stir the wet ingredients into the dry ingredients with a spatula until just combined.
Pour the batter into the tin and bake for 40 minutes until a skewer comes out clean.
Prick the warm cake deeply all over with a cocktail stick.
Mix the lemon juice and icing sugar then pour the drizzle over the hot cake.
Sprinkle with granulated sugar and extra lavender before cooling completely in the tin.