Preheat oven to 180°C / 356°F.
Peel the potatoes and cut them into wedges. About 4 cm (1.5-inch) thick.
Add them to a baking dish or baking pan that fits them almost in a single layer. It's okay if they are a bit overcrowded and a few slightly overlapping
Combine olive oil, mustard, and lemon juice in a small bowl. Drizzle over the potatoes.
Season with salt, pepper, and dried oregano.
Add also the garlic and toss to combine. Mix and toss the potatoes well, then spread them evenly.
Pour the water or stock in through the side of the pan so you don't rinse the potatoes.
Cover the pan with aluminum foil.
Bake for about an hour or until the potatoes are very tender.
Uncover and bake for 15-20 minutes more until there's only olive oil left in the pan and the potatoes turn slightly browned around the edges.
Serve with feta cheese for a simple, old-fashioned meal or with meat or fish dishes. They go with everything really!
TIP: If you let them sit for an hour or two before serving, they get even better!