Lightly grease a ~9×12in baking tin and preheat the oven to 180°C

Combine the butter, sugar, flour, baking powder, egg replacement, milk and lime zest in a large bowl and beat until smooth. If too dry, add a little warm water

Pour the mixture into the baking tin and cook for 35-40mins until the sponge is springy and it start to pull away from the sides of the tin.

After cooling for a bit, turn the sponge out onto a cooling rack

Once fully cooled, add the sugar into the lime juice and stir until mostly dissolved. Stab the sponge with a fork and spoon over the sugar-lime juice, keeping some back for later

Serve up a slice of sponge on a plate and spoon over some extra sugar-lime juice just before eating.