A handful of family homestays around town run hands-on cooking classes — typically a half-day session for around 3,500 LKR per person that produces five or six curries from scratch. You shop for the spices at the local market, grate coconut, temper the curry leaves, and eat what you cook. Several guesthouses on the main road advertise; ask around and pick a class that feels less than ten people.
A good rainy-afternoon activity and a practical introduction to a cuisine that can be hard to read from restaurant menus. Most teachers will write up the recipes for you to take home.