Select the area you want to dish
Copy/paste it until you're happy with the depth, moving it 1-2 pixels across each time. the first time you paste it,
dont move that layer
Select the first layer you pasted(the one you didnt move) then press shift+control+I to inverse the selection and select each pasted layer and delete the leftover outside
Layer>Flatten image to make it one layer, then smude on 50% strenght horizontally over the dished area then you're done