01 - Preheat the oven to 350°F. Line a 9 x 13 inch baking tin with parchment paper.
02 - Using a large bowl, cream the softened butter and caster sugar together until pale and fluffy.
03 - Beat in the eggs one at a time, mixing thoroughly after each addition.
04 - Fold in self-raising flour, poppy seeds, lemon zest, vanilla extract, and salt. Stir in milk until batter is smooth.
05 - Pour the mixture into the prepared tin and level the surface evenly.
06 - Bake for 28 to 32 minutes until golden and a skewer inserted in the center comes out clean.
07 - While baking, combine lemon juice and icing sugar to form the drizzle.
08 - Immediately after removing the baked cake, poke holes throughout with a skewer and drizzle the lemon mixture evenly over the surface.
09 - Allow the cake to cool completely in the tin before cutting into 12 squares for serving.