In a large, deep skillet, sauté garlic and onion in olive oil until garlic is light brown, about 5 minutes.
Add meat, curry, and fish sauce. Cook, stirring, until meat is browned and curry is fragrant, about 10-15 minutes.
Add the coconut milk, potatoes, and carrots.
Season with salt to taste.
Simmer, stirring occasionally, for about 1 hour.
Serve over rice topped with cashews.
Notes
Massaman curry paste: This will give you a bit of heat. If you like less heat, start with 2 tablespoons. If you like more heat, add more curry paste to taste.
Coconut milk: I've tried using lite coconut milk, but the sauce ended up watery.