Marinate the chicken for 10 minutes in the fish sauce, lemongrass, cornflour and brown sugar.
Heat oil in a saucepan or wok over medium-high heat.
Once hot, add the garlic and shallot and sauté for 3 minutes, stirring frequently.
Add the chicken and do not stir for 3 min. Then stir and wait 3 min. Repeat until browned.
Add coconut milk. Reduce well. The dish is finished when the sauce takes on a thick orange hue.
Notes
To prepare lemongrassCut 1 cm off the bottom of the lemongrass stem and remove the top with the thin leaves. Remove 1-2 outer layers, more if the stem is not fresh. Clean off any visible dirt with water. For use in stir-fries, slice the stalk into thin slices, almost like paper, to avoid a tough, fibrous texture.