My Rich & Easy(ish!) Homemade Demi-Glace - Chef YoYo

Ingredients

• 4 lbs beef bones (knuckles, shanks, femurs)
• 2 tbsp vegetable oil
• 2 large yellow onions, roughly chopped
• 2 large carrots, roughly chopped
• 2 celery stalks, roughly chopped
• 4 cloves garlic, smashed
• 1 tbsp tomato paste
• 1 tsp black peppercorns, crushed
• 1 bay leaf
• 2 sprigs fresh thyme
• 1 gallon cold water
• 1/2 cup dry red wine (optional, for deglazing)
• 1/4 cup dry sherry or Madeira wine (optional, for extra depth)
• (Optional) 1 tbsp unsalted butter