1. Cover the potato with water in a saucepan, add salt, and bring to a boil. Reduce the heat and cook until the potato is tender, about 10 minutes. Drain well.
2. Heat the oil in a large skillet over low heat. Add the onions and garlic. Cook, stirring, until the onions are translucent and tender, about 15 minutes.
3. Add the potato, beans, oregano, thyme, and coarse salt and pepper to taste. Cook, stirring, over berg low heat for 5 minutes. Let cool slightly.
4. Place half the bean mixture and 2 tbs crême fraîche in a food processor. Pulse 8-10 minutes until slightly smooth. Remove to a bowl and repeat with the remaining bean mixture and crême fraîche. Combine the batches and season generously with salt and pepper. Cool completely, then refrigerate covered until ready to use. Twenty minutes before serving, remove the slather from the refrigerator. Serve slathered on toasted peasant bread or pita chips.