Preheat oven to 325°F (160°C).
In a medium bowl, beat yogurt, egg yolks and 3 tbsp. sugar until smooth and creamy. Divide mixture evenly among four 1/2-cup/125-ml ramekins.
Place ramekins in a roasting pan and add hot water to come halfway up the sides of the ramekins, making sure no water goes into mixture. Bake for 25 minutes. Remove from oven and let cool on a rack, at room temperature, for at least 1 hour. Refrigerate until cold, if desired.
When ready to serve, evenly sprinkle remaining sugar over custards. Broil (or use a blow torch) until sugar turns golden brown. Garnish each ramekin with 1 tsp. (5 ml) toasted coconut, if desired.