Season beef with salt. Set aside. Heat oil in large wok or skillet on medium-high heat. Add beef and curry paste; stir fry 2 to 3 minutes or until beef is lightly browned.
Stir in coconut milk. Bring to simmer on medium heat, stirring frequently. Reduce heat to low. Stir in fish sauce and sugar. Simmer 10 to 15 minutes longer to blend flavours. Sprinkle with basil. Cover. Remove from heat. Let stand 5 minutes.
Garnish with additional basil and chile slices, if desired. Serve with cooked jasmine rice, if desired.
Partially freezing the steak makes it easier to cut into thin strips.
Thai basil has dark green leaves with purple stems and has a licorice flavor. It can be found in most Asian groceries. If unavailable, substitute Italian basil.