How to bake: this is the only recipe for lemon drizzle cake you'll ever need

Is there anything more delicious than a slice of lemon drizzle cake with a cup of tea?
If you subscribe to the idea that baking is a science and therefore not for you, then consider this lemon drizzle cake a mathematically perfect recipe.
Very difficult to get wrong, and still delicious even if it sinks in the middle (more on that later), lemon cake is what Americans call pound cake, and what Irish people call 'grab it before it's all gone.'