Grease 8-inch/20-cm loose-bottomed cake tin, and line with baking parchment. Or other well lined tin/dish of similar size will also work.
Preheat oven to 180C
Finely zest the lemon, then squeeze the juice into a separate container and set aside
Put the softened butter and 140g sugar into a mixing bowl. Beat together thoroughly until well combined. Beat in the eggs one at a time, followed by the vanilla extract and lemon zest.
Shortly before the cake comes out of the oven, gently warm the lemon juice with 2 tablespoons of sugar in a small saucepan. Stir until the sugar has dissolved.
Pour the warm lemon mixture over the cake while it is still hot. Leave to cool to room temperature before removing it from the tin and serving.