Slice onions and garlic. Season with ras el hanout, cumin, pimenton dulce.
Cook slowly in olive oil for 30–40 minutes. Do not let them colour.
Oil a gratin dish.
Slice potatoes thinly.
Layer the potatoes with onion and garlic.
Just about cover with stock.
Cook in a low oven for 60–90 minutes till the stock is close to being absorbed. The quality o