how to register an advance payment ?

[Bob Alexander]

I bought a piece of funiture for 1000 euros and as it needs to be custom
built the carpenter asked for an advance payment of 300 which I payed with
my credit card.

I therefore registered in gnucash a charge to my credit card of 300 with a
transfer on my "house" expense income.

So far so good, but what I would like to be able to track is that in some
time I will have to pay for another 700 and that the overall cost of that
good is 1000.

How would you go about it ?

Thank you
Robert