Heat a wok or large skillet over medium-high heat; whisk 1/2 cup coconut milk and curry paste together until simmering, 1 to 2 minutes. Stir in 1/4 cup coconut milk; return curry mixture to a simmer. Repeat with remaining coconut milk returning mixture to a simmer with each addition, 7 to 8 minutes altogether.
Stir chili paste and beef into curry mixture; simmer just until beef is slightly pink in the center, 4 to 5 minutes. Stir in basil and sugar; cook until beef is soft and cooked through, 3 to 5 minutes more. Serve with cooked rice.