FOR THE PONZU SAUCE:
½ cup soy sauce
¼ cup bonito flakes
2 tbsp. fresh lemon juice
2 tbsp. mirin
2 tbsp. rice vinegar
1 tbsp. fresh lime juice
1 (2") piece kombu
1 (2") piece ginger, peeled and grated

FOR THE STEAKS:
1 slice soft white sandwich bread, crust removed
3 tbsp. ketchup
3 tbsp. mayonnaise
1 tbsp. Worcestershire sauce
1 tsp. yellow mustard
1 egg
1 small white onion, grated
Kosher salt and freshly ground black pepper, to taste
1 lb. ground beef
½ lb. ground pork
1 tbsp. canola oil
¼ head green cabbage, shredded
½ medium daikon, peeled and finely grated
Kaiware (daikon) or other sprouts, for garnish (optional)
Cooked white rice, for serving (optional)