FILL with water half of a press cooker. Add the garlic clove and ¼ of onion.
HEAT over high heat. When it begins to boil add beans already clean.
COVER the pot and cook for 30 minutes after the pot starts whistling. Passed this time take away from heat. Let the pot get cool to open it.
HEAT butter in another pan without burning it.
FRY the chopped onion and add beans. Season with salt and let it boil, with an open pot for 10 minutes. Check the season and cooking. Take away from heat.
POUR a little of olive oil and a pinch of dried oregano on each plate before serving.