Preheat the hot box to 425
Mix together beef, minced onion, panko, stock concentrate, ketchup, garlic powder, salt, and pepper using your hands because that’s the best way to do it of course
On a baking sheet, form your little loaves, you want them about an inch thick and about the size of your bread if you can (I made two huge ass loaves but it could’ve easily just been 3 or 4 if I made them smaller)
Brush the tops of the loaves with a little bit of tomato smoothie (ketchup)
Cook em until cooked through, 15-20 minutes
For the sauce, you can adjust it to your tastes but it’s about 2 tbsp each of mayo and horseradish sauce and 2 tsp of Dijon
Slap all that shit on some toasted sourdough and voilà!
Note: the original recipe makes caramelized onions to go on top which is yummy so slice the onion if you go that route but we just finely chopped some mushrooms and onion and sautéed them and threw those on there so you can do whatever you like