Season beef cubes generously with salt and pepper. Heat 2 tablespoons oil in a large heavy-bottomed pot or Dutch oven over medium-high heat. Brown beef in batches, about 3-4 minutes per side, ensuring all sides are caramelized. Transfer browned beef to a plate and set aside.

Reduce heat to medium and add remaining 1 tablespoon oil to the same pot. Add sliced onions and cook, stirring occasionally, for 10-12 minutes until golden brown and caramelized. Add garlic and ginger, cooking for another minute until fragrant.

Return browned beef to the pot along with any accumulated juices. Add beef stock, scraping up any browned bits from the bottom of the pot. Bring to a boil, then reduce heat to low, cover, and simmer for 1 hour.

Add carrots and potatoes to the pot. Continue simmering, covered, for another 20-25 minutes until vegetables are tender and beef is fork-tender.

In a small bowl, mix the grated apple with soy sauce and mirin. Add this mixture to the curry along with the curry roux blocks. Stir gently until the roux completely dissolves and the curry thickens, about 5-8 minutes.

Taste and adjust seasoning with salt and pepper as needed. Let the curry rest for 5 minutes to allow flavors to meld. Serve hot over steamed white rice.