Potato Knishes Recipe

Ingredients

• 2 1/2 cups all-purpose flour
• 1 teaspoon baking powder
• 1/2 teaspoon salt
• 1/2 cup water
• 1/2 cup neutral oil (like vegetable or canola)
• 1 large egg, whisked
• 1 teaspoon white vinegar
• 3 tablespoons olive oil
• 1 medium yellow onion, chopped
• 1/4 teaspoon salt
• 1/2 teaspoon black pepper
• 1 pound russet potatoes, peeled and quartered
• 2 tablespoons unsalted butter
• 1 tablespoon water
• Mustard, for serving