Preheat oven to 180°C (350°F) and line a baking tray with parchment paper.
In a bowl, cream together butter and sugar until light and fluffy.
Beat in the egg, then add condensed milk, lemon zest, and lemon juice.
In a separate bowl, sift flour, baking powder, and salt.
Gradually fold dry ingredients into the wet mixture until a soft dough forms.
Roll dough into small balls and flatten gently with a fork.
Place on baking tray, leaving space between each biscuit.
Bake for 12–15 minutes or until light golden at the edges.
Cool on a wire rack before serving.