Pour 1 cup buttermilk into top half of a double boiler and sprinkle in gelatin. Allow to sit 5 minutes, until soft.
Meanwhile, line a strainer with cheesecloth. Fill bottom half of double boiler with water and bring to a simmer. Combine heavy cream and maple syrup in a small saucepan and bring to just a boil. Add cream and syrup mixture to buttermilk and gelatin mixture in top half o fdouble boiler, an dplace over bottom half with simmering water, whisking until gelatin is dissolved, about 4 minutes.
Stir in remaining 1 1/2 cups buttermilk. Pass through cheesecloth-lined strainer. Pour into 8 to 10 small custard cups or cordial glasses. Place plastic wrap on top of each container and refrigerate at least 5 hours.
Serve custard in cordial glasses, drizzle additional maple syrup on top.