Heat oil in a large heavy based skillet over medium high heat.
Add curry paste and and cook for about 2 minutes so it "dries out"
Add chicken broth and stir to dissolve paste. Simmer rapidly for 3 minutes or until liquid reduces by half.
Add coconut milk, lime leaves, sugar and fish sauce. Stir, then add chicken.
Spread chicken out, bring to simmer, then turn heat down to medium. Simmer for about 8- 10 minutes or until Sauce reduces, the chicken is cooked and the sauce is almost at the thickness you want.
Do a taste test. Add more fish sauce (or even shrimp paste) to add more saltiness, sugar for sweetness.
Add potatoes, green beans and mushrooms, stir. Cook for 3 minutes or until potatoes is just cooked through and Sauce is thickened.
Remove from heat. Stir through a handful of Thai basil leaves.
Serve overjasmine rice, garnished with fresh red chilli slices and fresh coriander/cilantro leaves, if desired.