How would you make an object look at another object but only on the y axis ( up or down ) ?

-- Example 
object.CFrame = CFrame.new(object.Position, anotherObject.Position)

This line of code would make the object face the other object. But how would I make it only face on the y axis? I tried this :

-- Example 2
object.CFrame = CFrame.new(object.Position, Vector3.new(object.Position.X, anotherObject.Position.Y, object.Position.Z))

But that would make the object face the other object but not "look" up or down. Its kind of difficult for me to explain. Here is a drawn example ; https://gyazo.com/9b8226bbaaaf797e7c4fdd8f18ae025f

--[ HAS BEEN SOLVED IN COMMENTS, dont know how to set comment as answer so ]--