Spawn objects instantly on the client

I am aware that in order to spawn objects over the network, one must call NetworkServer.Spawn() on the Server. However, say for example the client fires a projectile on mouse click. On the client side, we don't want to wait for the server to receive the command to spawn the projectile but rather spawn the projectile instantly on the client and then notify the server.

How can I go about doing this? (NetworkServer.Spawn() does not work on the client side)