1Preheat the oven to 350F.
2In a large bowl, stir together the butter and sugar, stir in the eggs, lemon zest and juice until well blended.
3In a small bowl, stir together the flour, baking powder and salt. Add half to the butter mixture, stir just until combined, then stir in the milk, then the remaining dry ingredients, stirring just until combined. Gently fold in the blackberries.
4Scrape the batter into a greased or parchment-lined 8x4-inch loaf pan. Bake for 50-60 minutes, until golden and springy to the touch. Cool in the pan on a wire rack. If you like, stir together the lemon juice and icing sugar and drizzle over the cake while still warm.