potato knish, two ways

INGREDIENTS

• 2 1/2 cups all-purpose flour
• 1 teaspoon baking powder
• 1/2 teaspoon table salt
• 1 large egg
• 1/2 cup vegetable oil (Joe also recommends schmaltz, or rendered chicken fat, if you’ve got some)
• 1 teaspoon white vinegar
• 1/2 cup water (see Update, above)
• 1 1/2 pounds (about 3 medium) russet potatoes, peeled and quartered
• 1 small yellow onion, peeled and diced small
• 1 tablespoon vegetable or olive oil
• 1 tablespoon unsalted butter
• Freshly ground black pepper
• 1 large egg yolk
• 1 teaspoon water
• 1 1/2 pounds medium red potato (about 3 to 4), peeled and quartered
• 1 big leek (about 1/2 pound), white and light-green parts only, halved lengthwise, and thinly sliced (you’ll clean the grit out in a moment)
• 1 generous cup lacinato kale ribbons (about 3 ounces or 1/4 to 1/3 bundle), tough stems and ribs removed and leaves cut into strips (you’ll wash it in a moment)
• 3 ounces cream cheese, at room temperature