Cheese Stuffed Japanese Hamburger Steak

Bahan-bahan (4 porsi)

• ½ onion ((5 oz, 142 g))
• 1 Tbsp neutral oil
• ¾ lb ground beef and pork combination
• ⅓ cup panko (Japanese breadcrumbs)
• 2 Tbsp milk
• 1 large egg (50 g w/o shell)
• ½ tsp nutmeg
• ½ tsp Diamond Crystal kosher salt
• freshly ground black pepper ((to taste))
• 1 slice Provolone cheese
• 1 Tbsp neutral oil
• 3 Tbsp red wine
• 1 Tbsp unsalted butter
• 3 Tbsp ketchup ((to taste))
• 3 Tbsp tonkatsu sauce
• 3 Tbsp red wine
• 3 Tbsp water