Place ginger and the lemongrass into a medium saucepan.
Add the heavy cream and simmer gently for 25 minutes to infuse the flavours.
Remove the infusion from the stove and strain through a fine sieve.
In a mixing bowl whisk together the yolks, the sugar the lemon extract and the bitters.
Slowly mix in the heavy cream infusion.
Pour into ramekins or an oven casserole dish. Remove any foam from the top of mixture with a teaspoon.
Place ramekins into a large casserole dish and pour hot water until the level is halfway up the sides of the ramekin dish. Put into oven and bake until the custard is firm (the center should jiggle just a little when you shake it) approximately 40 -50 minutes. Remove the ramekins from the water bath and completely cool before you cover with plastic wrap and refrigerate.
Sprinkle the top with granulated sugar and using a blow torch caramelize the sugar. The oven broiler can be used in place of the torch.
Place the ramekins in a tray of cold water and ice and leave in the broiler for 3-5 minutes--just enough to caramelize the sugar.
Variations: 1/4 teaspoon grated lime peel can be substituted for the lemon grass.