Heat oil in a wok over medium-high heat. Add curry paste.
Stir-fry for 30 seconds or until aromatic. Slowly pour in coconut milk, stirring constantly. Bring to the boil. Reduce heat to medium and simmer for 3 minutes.
Add sugar, fish sauce and 2 teaspoons lime juice. Stir to combine.
Wash and drain bok choy. Cut bok choy into quarters lengthways (if small, cut in half).
Line base of a steamer basket with baking paper. Place bok choy in basket. Steam, covered, over boiling water (do not allow steamer base to touch water) for 2 to 3 minutes or until thickest part of stems are tender (see shortcut). Transfer to a plate.
Pour curry sauce over bok choy and sprinkle with peanuts.