The secret ingredients are the key to a richer curry. Some are preference-based. Be sure to cut potatoes and carrots into obscure large shapes assuming you're able to simmer enough.
Peel potatoes and cut into large chunks. Soak in water for 15 minutes to remove excess starch. Cut carrots into chunks and onions into semi-large slices.
Cut beef into cubes and sprinkle with salt.
Preheat a large pot with oil over medium-high heat. Sear beef chunks until both sides are browned. Remove beef and set aside.
Don't rush the sear — good browning adds depth to the curry.
Add butter to the pot, then add onions. Sauté for a few minutes until softened.
Add minced garlic and sauté for 30 seconds until fragrant.
Add carrots and potatoes (drained). Stir for about 1 minute.
Return beef to the pot. Pour in 5 cups of water.
Add worcestershire sauce, ketchup, honey, and grated apple. Stir to combine. Cover with lid and simmer on medium heat for about 20 minutes, stirring occasionally.
These 4 secret ingredients add umami, sweetness, and acidity that deepen the curry.
Once vegetables and beef are cooked, turn off the heat. Add the curry roux, breaking it into smaller pieces so it dissolves completely. Stir until fully incorporated.
Turn off heat before adding roux to prevent scorching.
Turn heat back on to medium-low and simmer for another 15 minutes until the curry thickens.
Serve over steamed rice.