Grease four 5-ounce ramekins or baking dishes and coat with sugar, tapping out the excess. Ready a large bamboo steamer (available at kitchen stores or Asian food stores) over a pan of barely simmering water (steam should be visible when you lift the bamboo steamer lid and the water should not come through the steamer).
Heat the milk with the lemon zest, lemongrass, and ginger until it reaches a gentle simmer. Simmer for 10 minutes, then remove from the heat, strain and cool to just above room temperature.
Stir the flour, the ¼ cup of sugar and salt in a small bowl and set aside.
In a separate bowl, whisk the egg yolks and lemon juice by hand until frothy and pale (not doubled in volume). Whisk in the milk, then sift the flour mixture over and whisk in.
In another bowl, whip the whites until frothy, then add the remaining 2 tbsp of sugar and continue whipping until the whites hold a soft peak when the beaters are lifted. Use a whisk to fold the whites into the batter in 2 additions. Pour the batter into the prepared ramekins.
Place the ramekins into the steamer and cover with the lid immediately. Let the soufflé cakes steam for about 25 minutes, taking care that the water underneath the steamer does not boil or simmer vigorously, until the cake soufflés to the top of the ramekin.
The cakes can be served warm, right from the steamer and in their dish, or cooled to room temperature and turned out. Serve with fresh berries.