Preheat oven to 350°F (175°C) and grease an 8x8-inch baking pan or line with parchment paper.
In a bowl, whisk together flour, baking powder, poppy seeds, and salt.
In another bowl, cream softened butter and sugar until light and fluffy (about 3 minutes).
Beat in eggs one at a time, then stir in lemon juice and zest until combined.
Gradually mix dry ingredients into the wet mixture until just combined; do not overmix.
Pour batter into prepared pan and bake for 25-30 minutes or until a toothpick comes out clean.
Allow to cool before glazing by mixing powdered sugar and lemon juice until smooth; pour over cooled bars.
