For beer dressing:
To make the salad:
Cook the potatoes in salted water, about 20-25 minutes. Meanwhile preapre dressing.
To make the dressing:
Heat 2 tablespoons of the olive oil in a small frying pan over medium heat. Add the onions and cook until just soft, about 5 minutes. Add the lager, vinegar, and sugar and boil for 5 minutes. Put into a food processor with the mustard. With the motor running, slowly pour in the remaining 4 tablespoons olive oil. Taste for salt and pepper.
When potatoes are soft and cooled down a bit, slice them, into 5mm rounds. While the potatoes are still warm, gently mix them with the onions, parsley, and beer dressing. Do not overmix or the potatoes may break into pieces.
Taste for salt and pepper. Garnish with chopped chives. Serve warm or at room temperature.