Preheat oven to 180°C (160°C fan/350°F) and line a 12-hole muffin tin with paper liners.
Beat the softened butter and caster sugar together in a stand mixer until light, pale, and fluffy.
Add eggs one at a time, beating thoroughly after each addition to maintain the emulsion.
Sift in the self-raising flour and salt, then fold gently with a spatula until just incorporated.
Fold in the lemon zest and milk until the batter reaches a dropping consistency.
Distribute the batter evenly across the 12 cupcake liners using a portion scoop.
Bake for 18 to 20 minutes until the sponges are golden and spring back when touched.
Prepare the drizzle by whisking the lemon juice and granulated sugar together in a small bowl.
Remove cupcakes from the oven and immediately prick the surface of each sponge multiple times with a skewer.
Spoon the lemon drizzle over the hot cupcakes while still in the tin to allow the syrup to soak in.
Cool in the tin for 10 minutes before transferring to a wire rack to cool completely.