Serves 4 - 6
In a medium pot, boil five cups chopped potatoes until tender. Drain and set aside to cool. In a bowl, mix one cucumber, chopped into half moon slivers, 1 cup purslane leaves and buds, (flowers and stalks are edible as well if you choose) and 1 cup chopped scallions with greens. Add potatoes and mix well.
In a small wide bowl mix one egg yolk until smooth. Drip in, whisking constantly, 1 cup olive oil making sure to add slowly enough to keep mixture opaque. Add 1 teaspoon salt and 1-2 finely chopped serano peppers. Mix well. Spoon over potato and vegetable mixture (there may be some spicy mayo leftover; it will keep in the fridge for at least a week) adding several teaspoons white wine or cider vinegar and fresh ground pepper and salt to taste. Toss well and serve at room temperature.