forget the part of baking the tart and the foie togheter!
a foie is "baked" at 60°celsius , a tart at 200° celsius.
at 200°c the foie will loose all fat and get gray!
here a possible way:
bake the tart "blind", that meens after you put the dought into the form, place a baking-paper on top and fill up with cheap-dry-beens, so that the tart stay down. bake all togeter for about 15 minutes, take it out and extract the beans and paper, bake until done.
make a vegetabil-fond, pass it to a towel, so all is clear and fat-free. add sautern as you like, add agar-agar (you can get it at drugstore) is't a gelatine from seaweat.
let it become cold in refridgerator.
cut in small pieces.
if you use a frsch foie, search a recepie for a terrine, if you use all ready a prepared you couls cut in slices
take the cold tart, place a spoon cold gelatine into, and place a slice foie on top, decorate with fresh herbs as you like.