Mile End's Knishes

INGREDIENTS

• 2 pounds russet potatoes (about 4 potatoes), scrubbed clean
• 1 1/2 pounds yukon gold potatoes (6 to 8 potatoes), scrubbed clean
• 2 parsnips, peeled and roughly chopped
• 1/2 celery root, peeled, trimmed, and roughly chopped
• 2 medium white onions, roughly chopped
• 3 tablespoons
• or canola oil
• 2 fresh bay leaves
• Diamond Crystal kosher salt and freshly ground black pepper
• 3 large eggs
•  
• 8 large eggs, beaten
• 3/4 cup
• , at room temperature, or canola oil
• 5 1/3 cups all-purpose flour (reduce flour to 5 cups if using canola oil)
• 4 teaspoons baking powder
• 2 teaspoons Diamond Crystal kosher salt
• 1 additional large egg, beaten, for the egg wash
• Poppy seeds, sesame seeds, caraway seeds, or other toppings of your choice
• Spicy brown mustard, such as Gulden's, for serving