Preheat the oven to 180°C (160°C fan/Gas Mark 4). Grease a 2 lb loaf tin and line with baking parchment, leaving an overhang.
In a large bowl, combine 175 g self-raising flour, 175 g caster sugar, 175 g unsalted butter (softened), 3 large eggs, and the zest of 1 large lemon. Beat with an electric mixer for 2–3 minutes until smooth and fluffy.
Spoon the batter into the prepared tin and level the top with the back of a spoon or spatula.
Bake for 45–50 minutes, until the top is golden brown, the cake feels springy, and a skewer inserted into the centre comes out clean.
While the cake bakes, mix 100 g caster sugar with 4.5 tablespoons freshly squeezed lemon juice until the sugar is mostly dissolved.
When the cake comes out hot, poke holes all over the top with a skewer or fork, then pour the lemon drizzle evenly over the cake, letting it soak in.
Leave the cake in the tin to cool completely on a wire rack, then lift out using the parchment overhang, slice, and serve.