Defrost blueberries at room temperature. Finely puree 200 g blueberries with coconut milk, stir in lime juice and lime zest. Chill the rest of the blueberries. Line an ovenproof dish (17.5 x 26 cm; 2 litres capacity) with baking paper.
For the ice cream mixture, whisk the eggs, salt and Stevia with a hand mixer for 6-8 minutes until thick and creamy. Stir the blueberry mixture into the egg mixture. Pour the ice cream mixture into the prepared mould.
Put the parfait in the freezer for at least 6 hours, preferably overnight.
Remove the ice cream from the cooler about 15 minutes before serving. Using the baking paper, lift it out of the mould and cut it into pieces. Spread the rest of the blueberries on top. Decorate with lemon balm if desired and serve immediately.