Add 1½ teaspoon fish sauce and the oil to the beef and massage it in with your hands, separating the pieces of beef that are stuck together as you mix.
In a saute pan or a wok over medium high heat, reduce ¾ cup of coconut milk until thickened and creamy.
Stir in the curry paste and reduce the heat to medium low.
Cook the paste for a few minutes, stirring constantly, until the coconut oil separates away from the paste. If the paste sticks to the pan, you can deglaze with a bit of the remaining coconut milk.
Add the palm sugar and torn kaffir lime leaves and cook for a minute or so until the sugar is dissolved.
Add the beef and quickly toss it with the curry paste, separating the pieces of beef as much as you can.
Once the beef is about 50% cooked, add the remaining coconut milk and stir for 30 more seconds or just until the beef is fully cooked. If it looks too dry, you can add a splash of water at this point.
Stir in the red bell peppers, if using, and turn off the heat.
Taste and adjust the seasoning with more fish sauce and/or sugar as needed.
Garnish with julienned kaffir lime leaves and more red peppers as desired.
Serve with jasmine rice, enjoy!