Kroket Panggang

Bahan-bahan (15 porsi)

• 2 lb russet potatoes ((about 4 potatoes))
• 1 onion
• 3 Tbsp neutral oil ((divided))
• 1 lb ground beef
• freshly ground black pepper
• ¼ tsp Diamond Crystal kosher salt ((for the beef))
• 2½ cups panko (Japanese breadcrumbs)
• ½ tsp Diamond Crystal kosher salt ((for the potatoes))
• 1 Tbsp unsalted butter
• 3 large eggs (50 g w/o shell) ((beaten))
• ½ cup all-purpose flour (plain flour)
• tonkatsu sauce ((or make my Homemade Tonkatsu Sauce))