In a medium-high heat, simmer 1 can of coconut milk for 15 mins to achieve the thick and creamy consistency. If your coconut comes as a big solid lump in water, use only the milk and discard the coconut water. The coconut water will prolong the simmering time.
While the coconut milk is thickening, slice up peppers, lime leaves, and thinly sliced beef. Set aside.
Once the coconut milk is thickened, add in the panang curry paste, fish sauce, and sugar. Cook on a medium-low heat for about 7 minutes. Stir often.
Turn up the heat to medium. Add the beef and cook for 10 minutes or until the beef is done.
Sprinkle in sliced peppers and lime leaves. Enjoy!