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
• 1/4 cup water, or more if needed
• 1 1/2 pounds russet potatoes, peeled and quartered
• 1 small yellow onion, peeled and diced small
• 1 tablespoon vegetable or olive oil
• 1 tablespoon unsalted butter
• 1/2 teaspoon table salt
• freshly ground black pepper
• 1 large egg yolk
• 1 teaspoon water
• 1 1/2 pounds medium red potato, peeled and quartered
• 1 tablespoon vegetable or olive oil
• 1 tablespoon unsalted butter
• 1/2 teaspoon table salt
• freshly ground black pepper
• 3 ounces cream cheese, at room temperature